U.S. patent application number 14/405465 was filed with the patent office on 2015-05-21 for mobile communication system and user terminal.
This patent application is currently assigned to KYOCERA CORPORATION. The applicant listed for this patent is KYOCERA CORPORATION. Invention is credited to Kugo Morita, Chiharu Yamazaki.
Application Number | 20150139176 14/405465 |
Document ID | / |
Family ID | 49712117 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150139176 |
Kind Code |
A1 |
Morita; Kugo ; et
al. |
May 21, 2015 |
MOBILE COMMUNICATION SYSTEM AND USER TERMINAL
Abstract
In a mobile communication system that supports D2D communication
in which radio communication is directly performed between a first
user terminal and a second user terminal in a frequency and a time
assigned from a base station, in a time in which data is to be
received from the first user terminal, when the second user
terminal does not receive the data from the first user terminal,
the second user terminal transmits failure notification indicating
reception failure in the D2D communication to the base station.
Inventors: |
Morita; Kugo; (Yokohama-shi,
JP) ; Yamazaki; Chiharu; (Ota-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA CORPORATION |
Kyoto |
|
JP |
|
|
Assignee: |
KYOCERA CORPORATION
Kyoto
JP
|
Family ID: |
49712117 |
Appl. No.: |
14/405465 |
Filed: |
June 6, 2013 |
PCT Filed: |
June 6, 2013 |
PCT NO: |
PCT/JP2013/065748 |
371 Date: |
December 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61656194 |
Jun 6, 2012 |
|
|
|
61693993 |
Aug 28, 2012 |
|
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Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04W 76/23 20180201;
H04W 8/005 20130101; H04W 72/0446 20130101; H04L 47/746 20130101;
H04W 72/0453 20130101; H04W 76/14 20180201; H04L 5/0055
20130101 |
Class at
Publication: |
370/330 |
International
Class: |
H04W 76/02 20060101
H04W076/02 |
Claims
1. A mobile communication system comprising a first user terminal
and a second user terminal, wherein D2D communication is radio
communication is directly performed between the first user terminal
and the second user terminal in a frequency and a time assigned
from a base station, and in a time in which data is to be received
from the first user terminal, when the second user terminal does
not receive the data from the first user terminal, the second user
terminal transmits failure notification indicating reception
failure in the D2D communication to the base station.
2. The mobile communication system according to claim 1, wherein,
in a time in which data is to be transmitted to the second user
terminal, when there is no data to be transmitted to the second
user terminal, the first user terminal transmits predetermined data
to the second user terminal.
3. The mobile communication system according to claim 2, wherein,
in the time in which the data is to be transmitted to the second
user terminal, when there is no data to be transmitted to the
second user terminal and a passage time after data is finally
transmitted to the second user terminal is smaller than a threshold
value, the first user terminal repeatedly transmits the finally
transmitted data as the predetermined data.
4. The mobile communication system according to claim 2, wherein,
in the time in which the data is to be transmitted to the second
user terminal, when there is no data to be transmitted to the
second user terminal and a passage time after data is finally
transmitted to the second user terminal is equal to or more than a
threshold value, the first user terminal transmits dummy data as
the predetermined data.
5. The mobile communication system according to claim 1, wherein in
a time in which data is to be transmitted to the second user
terminal, when there is no data to be transmitted to the second
user terminal, the first user terminal transmits, to the base
station, data notification indicating that there is no data to be
transmitted to the second user terminal, and after the base station
receives the data notification from the first user terminal, when
the base station receives the failure notification from the second
user terminal, the base station ignores the failure notification
from the second user terminal.
6. The mobile communication system according to claim 1, wherein,
when the second user terminal determines that the reception failure
is caused by interference from another D2D communication, the
second user terminal includes information on the other D2D
communication into the failure notification, and transmits the
failure notification to the base station.
7. A user terminal that performs D2D communication which is radio
communication is directly performed with another user terminal in a
frequency and a time assigned from a base station, comprising: a
notification transmission unit that transmits failure notification
indicating reception failure in the D2D communication to the base
station when data is not received from the other user terminal in a
time in which the data is to be received from the other user
terminal.
8. A user terminal that performs D2D communication which is radio
communication is directly performed with another user terminal in a
frequency and a time assigned from a base station, comprising: a
data transmission unit that transmits predetermined data to the
other user terminal when there is no data to be transmitted to the
other user terminal in a time in which the data is to be
transmitted to the other user terminal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a mobile communication
system and a user terminal, which are used in a mobile
communication system supporting D2D communication.
BACKGROUND ART
[0002] In 3GPP (3rd Generation Partnership Project) which is a
project aiming to standardize a mobile communication system, the
introduction of Device to Device (D2D) communication is discussed
as a new function after release 12 (see Non-Patent Document 1).
[0003] In the D2D communication, a plurality of user terminals
proximal to one another are able to perform direct communication
with each other in the state where a radio connection with a
network is established (in the state where synchronization is
achieved). In addition, the D2D communication is also called
Proximity Service communication.
PRIOR ART DOCUMENT
Non-Patent Document
[0004] Non-Patent Document 1: 3GPP technical report "TR 22.803
V0.3.0" May 2012
SUMMARY OF THE INVENTION
[0005] However, the current 3GPP standards do not define
specifications for appropriately controlling the D2D communication.
Thus, there is a problem that the D2D communication and the
cellular communication (radio communication between a user terminal
and a base station) are difficult to be compatible with each
other.
[0006] Therefore, the present invention is to provide a mobile
communication system and a user terminal, with which it is possible
to appropriately control D2D communication.
[0007] According to an embodiment, in a mobile communication system
that supports D2D communication in which radio communication is
directly performed between a first user terminal and a second user
terminal in a frequency and a time assigned from a base station, in
a time in which data is to be received from the first user
terminal, when the second user terminal does not receive the data
from the first user terminal, the second user terminal transmits
failure notification indicating reception failure in the D2D
communication to the base station.
[0008] According to an embodiment, a user terminal that supports
D2D communication in which radio communication is directly
performed with another user terminal in a frequency and a time
assigned from a base station, comprises a notification transmission
unit that transmits failure notification indicating reception
failure in the D2D communication to the base station when data is
not received from the other user terminal in a time in which the
data is to be received from the other user terminal.
[0009] According to an embodiment, a user terminal that supports
D2D communication in which radio communication is directly
performed with another user terminal in a frequency and a time
assigned from a base station, comprises a data transmission unit
that transmits predetermined data to the second user terminal when
there is no data to be transmitted to the second user terminal in a
time in which the data is to be transmitted to the second user
terminal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a configuration diagram of an LTE system.
[0011] FIG. 2 is a block diagram of UE.
[0012] FIG. 3 is a block diagram of eNB.
[0013] FIG. 4 is a protocol stack diagram of a radio interface in
the LTE system.
[0014] FIG. 5 is a configuration diagram of a radio frame used in
the LTE system.
[0015] FIG. 6 illustrates a data path in cellular
communication.
[0016] FIG. 7 illustrates a data path in D2D communication.
[0017] FIG. 8 is a sequence diagram of a search operation pattern 1
according to an embodiment.
[0018] FIG. 9 is a sequence diagram of a search operation pattern 2
according to the embodiment.
[0019] FIG. 10 is a flow diagram of a determination operation of a
method of assigning radio resource according to the embodiment.
[0020] FIG. 11 is a diagram for explaining a radio resource
assignment operation according to the embodiment (part 1).
[0021] FIG. 12 is a diagram for explaining a radio resource
assignment operation according to the embodiment (part 2).
[0022] FIG. 13 is a diagram for explaining a radio resource
assignment operation according to the embodiment (part 3).
[0023] FIG. 14 is a diagram for explaining transmission power
control and retransmission control according to the embodiment.
[0024] FIG. 15 is a sequence diagram when transmission power in the
D2D communication exceeds maximum transmission power.
[0025] FIG. 16 is a diagram for explaining an interference
avoidance operation according to the embodiment (part 1).
[0026] FIG. 17 is a diagram for explaining an interference
avoidance operation according to the embodiment (part 2).
[0027] FIG. 18 is a flow diagram of an operation pattern 1 of an
interference avoidance operation according to the embodiment.
[0028] FIG. 19 is a flow diagram of an operation pattern 2 of the
interference avoidance operation according to the embodiment.
[0029] FIG. 20 is a sequence diagram of the operation pattern 2 of
the interference avoidance operation according to the
embodiment.
DESCRIPTION OF THE EMBODIMENT
Overview of Embodiment
[0030] A mobile communication system according to an embodiment
supports D2D communication in which radio communication is directly
performed between a first user terminal and a second user terminal
in a frequency and a time assigned from a base station.
[0031] In a time in which the second user terminal does not receive
data from the first user terminal, when the data is not received
from the first user terminal, the second user terminal transmits
failure notification indicating reception failure in the D2D
communication to the base station.
[0032] In this way, the base station is able to recognize a
generation status of the reception failure in the D2D
communication, thereby taking measures to solve the reception
failure. Consequently, it is possible to appropriately control the
D2D communication in consideration of the generation status of the
reception failure in the D2D communication.
[0033] Ina time in which data is to be transmitted to the second
user terminal, when there is no data to be transmitted to the
second user terminal, the first user terminal may transmit
predetermined data to the second user terminal.
[0034] In this way, it is possible to prevent erroneous
determination that reception failure occurs in the second user
terminal.
[0035] In the time in which the data is to be transmitted to the
second user terminal, when there is no data to be transmitted to
the second user terminal and a passage time after data is finally
transmitted to the second user terminal is smaller than a threshold
value, the first user terminal may repeatedly transmit the finally
transmitted data as the predetermined data.
[0036] In this way, it is possible to prevent erroneous
determination in the second user terminal, and to improve the
reliability of communication by allowing the second user terminal
to repeatedly receive the same data. For example, the second user
terminal synthesizes the same data repeatedly received, thereby
enhancing a decoding success rate of the data.
[0037] In the time in which the data is to be transmitted to the
second user terminal, when there is no data to be transmitted to
the second user terminal and the passage time after the data is
finally transmitted to the second user terminal is equal to or more
than the threshold value, the first user terminal may transmit
dummy data as the predetermined data.
[0038] In this way, when a long time passes after the data is
finally transmitted, the dummy data is transmitted instead of
repetitive transmission, so that it is possible to prevent
meaningless repetitive transmission.
[0039] Alternatively, in the time in which the data is to be
transmitted to the second user terminal, when there is no data to
be transmitted to the second user terminal, the first user terminal
may transmit, to the base station, data notification indicating
that there is no data to be transmitted to the second user
terminal.
[0040] In this case, after the base station received the data
notification from the first user terminal, when the base station
received the failure notification from the second user terminal,
the base station ignores the failure notification from the second
user terminal.
[0041] In this way, it is possible to prevent determination that
reception failure has occurred from being erroneously made in the
base station.
[0042] When the second user terminal determines that the reception
failure is caused by interference from another D2D communication,
the second user terminal may include information on the other D2D
communication into the failure notification, and transmit the
failure notification to the base station.
[0043] In this way, the base station is able to recognize a
generation status of the reception failure in the D2D
communication, and to estimate a generation cause of the reception
failure.
Embodiment
[0044] Hereinafter, a description will be provided for an
embodiment in which D2D communication is introduced to a mobile
communication system (hereinafter, an "LIE system") configured in
conformity to the 3GPP standards, with reference to the
accompanying drawings, below.
[0045] (1) Overview of LTE System
[0046] FIG. 1 is a configuration diagram of an LTE system according
to the present embodiment.
[0047] As illustrated in FIG. 1, the LTE system includes a
plurality of UEs (User Equipments) 100, E-UTRAN (Evolved Universal
Terrestrial Radio Access Network) 10, and EPC (Evolved Packet Core)
20. In the present embodiment, the E-UTRAN 10 and the EPC 20
configure a network.
[0048] The UE 100 is a mobile radio communication device and
performs radio communication with a cell (a serving cell) with
which a radio connection is established. The UE 100 corresponds to
a user terminal.
[0049] The E-UTRAN 10 includes a plurality of eNBs 200 (evolved
Node-Bs). The eNB 200 corresponds to a base station. The eNB 200
manages a cell and performs radio communication with the UE 100
which is established a radio connection with the cell.
[0050] In addition, the "cell" is used as a term indicating a
minimum unit of a radio communication area, and is also used as a
term indicating a function of performing radio communication with
the UE 100.
[0051] The eNB 200, for example, has a radio resource management
(RRM) function, a routing function of user data, and a measurement
control function for mobility control and scheduling.
[0052] The EPC 20 includes MME (Mobility Management Entity)/S-GW
(Serving-Gateway) 300 and OAM 400 (Operation and Maintenance).
[0053] The MME is a network node that performs various types of
mobility control and the like for the UE 100 and corresponds to a
control station. The S-GW is a network node that performs transfer
control of user data and corresponds to a mobile switching
center.
[0054] The eNBs 200 are connected mutually via an X2 interface.
Furthermore, the eNBs 200 are connected to the MME/S-GW 300 via an
S1 interface.
[0055] The OAM 400 is a server device managed by an operator and
performs maintenance and monitoring of the E-UTRAN 10.
[0056] Next, the configurations of the UE 100 and the eNB 200 will
be described.
[0057] FIG. 2 is a block diagram of the UE 100. As illustrated in
FIG. 2, the UE 100 includes an antenna 101, a radio transceiver
110, a user interface 120, a GNSS (Global Navigation Satellite
System) receiver 130, a battery 140, a memory 150, and a processor
160. The memory 150 corresponds to a storage medium.
[0058] The UE 100 may not have the GNSS receiver 130. Furthermore,
the memory 150 may be integrally formed with the processor 160, and
this set (that is, a chipset) may be called a processor 160'.
[0059] The antenna 101 and the radio transceiver 110 are used for
transmission/reception of a radio signal. The antenna 101 includes
a plurality of antenna elements. The radio transceiver 110 converts
a baseband signal output from the processor 160 into a radio
signal, and transmits the radio signal from the antenna 101.
Furthermore, the radio transceiver 110 converts a radio signal
received in the antenna 101 into a baseband signal, and outputs the
baseband signal to the processor 160.
[0060] The user interface 120 is an interface with a user carrying
the UE 100, and for example, includes a display, a microphone, a
speaker, and various buttons and the like. The user interface 120
receives an operation from a user and outputs a signal indicating
the content of the operation to the processor 160.
[0061] The GNSS receiver 130 receives a GNSS signal in order to
obtain location information indicating a geographical location of
the UE 100, and outputs the received signal to the processor
160.
[0062] The battery 140 accumulates power to be supplied to each
block of the UE 100.
[0063] The memory 150 stores a program to be executed by the
processor 160 and information to be used for a process by the
processor 160.
[0064] The processor 160 includes a baseband processor configured
to perform modulation/demodulation, coding/decoding and the like of
the baseband signal, and CPU (Central Processing Unit) configured
to perform various processes by executing the program stored in the
memory 150. Moreover, the processor 160 may include a codec
configured to perform coding/decoding of a voice/video signal.
[0065] The processor 160, for example, implements various
communication protocols which will be described later, as well as
implementing various applications. Details of the processes
performed by the processor 160 will be described later.
[0066] FIG. 3 is a block diagram of the eNB 200. As illustrated in
FIG. 3, the eNB 200 includes an antenna 201, a radio transceiver
210, a network interface 220, a memory 230, and a processor 240.
Note that the memory 230 may be integrally formed with the
processor 240, and this set (that is, a chipset) may be called a
processor.
[0067] The antenna 201 and the radio transceiver 210 are used for
transmission/reception of a radio signal. The antenna 201 includes
a plurality of antenna elements. The radio transceiver 210 converts
a baseband signal output from the processor 240 into a radio
signal, and transmits the radio signal from the antenna 201.
Furthermore, the radio transceiver 210 converts a radio signal
received in the antenna 201 into a baseband signal, and outputs the
baseband signal to the processor 240.
[0068] The network interface 220 is connected to the neighboring
eNB 200 via the X2 interface and is connected to the MME/S-GW 300
via the S1 interface. The network interface 220 is used in
communication performed on the X2 interface and communication
performed on the S1 interface.
[0069] The memory 230 stores a program to be executed by the
processor 240 and information to be used for a process by the
processor 240.
[0070] The processor 240 includes a baseband processor configured
to perform modulation/demodulation, coding/decoding and the like of
the baseband signal, and CPU configured to perform various
processes by executing the program stored in the memory 230.
[0071] The processor 240, for example, implements various
communication protocols which will be described later. Details of
the processes performed by the processor 240 will be described
later.
[0072] FIG. 4 is a protocol stack diagram of a radio interface in
the LTE system.
[0073] As illustrated in FIG. 4, the radio interface protocol is
classified into a layer 1 to a layer 3 of an OSI reference model,
wherein the layer 1 is a physical (PHY) layer. The layer 2 includes
a MAC (Medium Access Control) layer, an RLC (Radio Link Control)
layer, and a PDCP (Packet Data Convergence Protocol) layer. The
layer 3 includes an RRC (Radio Resource Control) layer.
[0074] The PHY layer performs coding/decoding,
modulation/demodulation, antenna mapping/demapping, and resource
mapping/demapping. The PHY layer provides a transmission service to
an upper layer by using a physical channel. Between the PHY layer
of the UE 100 and the PHY layer of the eNB 200, data is transmitted
through the physical channel.
[0075] The MAC layer performs preferential control of data, and a
retransmission process and the like by hybrid ARQ (HARQ). Between
the MAC layer of the UE 100 and the MAC layer of the eNB 200, data
is transmitted through a transport channel. The MAC layer of the
eNB 200 includes a MAC scheduler for determining a transport format
(a transport block size, a modulation and coding scheme, and the
like) and a resource block of an uplink and a downlink.
[0076] The RLC layer transmits data to an RLC layer of a reception
side by using the functions of the MAC layer and the PHY layer.
Between the RLC layer of the UE 100 and the RLC layer of the eNB
200, data is transmitted through a logical channel.
[0077] The PDCP layer performs header compression/extension and
encryption/decryption.
[0078] The RRC layer is defined only in a control plane. Between
the RRC layer of the UE 100 and the RRC layer of the eNB 200, data
is transmitted through a radio bearer. The RRC layer controls the
logical channel, the transport channel, and the physical channel in
response to establishment, re-establishment, and release of the
radio bearer. When there is an RRC connection between RRC of the UE
100 and RRC of the eNB 200, the UE 100 is in an RRC connected
state. Otherwise, the UE 100 is in an RRC idle state.
[0079] A NAS (Non-Access Stratum) layer positioned above the RRC
layer performs session management, mobility management and the
like.
[0080] FIG. 5 is a configuration diagram of a radio frame used in
the LTE system. In the LTE system, OFDMA (Orthogonal Frequency
Division Multiplexing Access) is employed in a downlink, and
SC-FDMA (Single Carrier Frequency Division Multiple Access) is
employed in an uplink, respectively.
[0081] As illustrated in FIG. 5, the radio frame includes 10
subframes arranged in a time-period direction, wherein each
subframe includes two slots arranged in the time-period direction.
Each subframe has a length of 1 ms and each slot has a length of
0.5 ms. Each subframe includes a plurality of resource blocks (RBs)
in a frequency direction, and a plurality of symbols in the
time-period direction. Each symbol is provided at a head thereof
with a guard interval called a cyclic prefix (CP).
[0082] In the downlink, an interval of several symbols at the head
of each subframe is a control region mainly used as a physical
downlink control channel (PDCCH). Furthermore, the other interval
of each subframe is a region mainly used as a physical downlink
shared channel (PDSCH).
[0083] In the uplink, both end portions in the frequency direction
of each subframe are control regions mainly used as a physical
uplink control channel (PUCCH). Furthermore, the center portion in
the frequency direction of each subframe is a region mainly used as
a physical uplink shared channel (PUSCH).
[0084] (2) Overview of D2D Communication
[0085] Next, the LTE system will be described with comparing the
normal communication (the cellular communication) with the D2D
communication.
[0086] FIG. 6 illustrates a data path in the cellular
communication. Furthermore, FIG. 6 illustrates the case in which
the cellular communication is performed between UE (A) 100-1 which
is established a radio connection with eNB 200-1 and UE (B) 100-2
which is established a radio connection with eNB 200-2. In
addition, the data path indicates a data transfer path of user data
(a user plane).
[0087] As illustrated in FIG. 6, the data path of the cellular
communication passes through the network. Specifically, the data
path via the eNB 200-1, the S-GW 300, and the eNB 200-2 is set.
[0088] FIG. 7 illustrates a data path in the D2D communication.
Furthermore, FIG. 7 illustrates the case in which the D2D
communication is performed between the UE (A) 100-1 which is
established a radio connection with the eNB 200-1 and the UE (B)
100-2 which is established a radio connection with the eNB
200-2.
[0089] As illustrated in FIG. 7, the data path of the D2D
communication does not pass through the network. That is, direct
radio communication is performed between the UEs. In this way, when
the UE (B) 100-2 exists in the vicinity of the UE (A) 100-1, the
D2D communication is performed between the UE (A) 100-1 and the UE
(B) 100-2, thereby obtaining an effect that a traffic load of the
network and a battery consumption amount of the UE 100 are reduced
and so on.
[0090] In addition, the D2D communication is assumed to be
performed in the frequency band of the LTE system, and for example,
in order to avoid interference to the cellular communication, the
D2D communication is performed under the control of the
network.
[0091] (3) Operation According to Embodiment
[0092] Hereinafter, the operation according to the embodiment will
be described.
[0093] (3.1) Search Operation
[0094] The UE (A) desiring to start the D2D communication should
have a (Discover) function of discovering the UE (B) that is a
communication partner existing in the vicinity of the UE (A).
Furthermore, the UE (B) should have a (Discoverable) function of
being discovered by the UE (A).
[0095] In the present embodiment, the UE (A) periodically transmits
a search signal (a Discover signal) to around the UE (A) in order
to discover the UE (B) that is a communication partner. In order to
be discovered by the UE (A), the UE (B) waits for the search signal
and transmits a response signal to the UE (A) in response to the
reception of the search signal. Then, the network determines
whether the D2D communication by the UE (A) and the UE (B) is
possible.
[0096] (3.1.1) Operation Pattern 1
[0097] FIG. 8 is a sequence diagram of a search operation pattern 1
according to the present embodiment.
[0098] As illustrated in FIG. 8, in step S1, the UE (A) 100-1
transmits a search signal to around the UE (A) 100-1. The search
signal includes an identifier of the UE (A) 100-1 and an identifier
of an application to be used in the D2D communication. The
identifier of the application, for example, is used in order to
limit UE (UE which will transmit a response signal) which will
respond to the search signal. The search signal may further include
an identifier of the UE (B) 100-2 that is a communication partner,
or an identifier of a group (a D2D communication group) of the UE
100 which will perform the D2D communication. Furthermore, when
transmitting the search signal, the UE (A) 100-1 stores
transmission power of the search signal.
[0099] The UE (B) 100-2 waits for the search signal and receives
the search signal from the UE (A) 100-1. The UE (B) 100-2 measures
received power (reception strength) of the search signal and stores
the measured received power.
[0100] In step S2, the UE (B) 100-2 transmits a response signal to
the UE (A) in response to the reception of the search signal. The
response signal includes an identifier of the UE (B) 100-2 and an
identifier of an application to be used in the D2D communication.
Furthermore, when transmitting the response signal, the UE (B)
100-2 stores transmission power of the response signal.
[0101] The UE (A) 100-1 waits for the response signal and receives
the response signal from the UE (B) 100-2. The UE (A) 100-1
measures received power (reception strength) of the response signal
and stores the measured received power.
[0102] In step S3, in response to the reception of the response
signal, the UE (A) 100-1 transmits, to the eNB 200, a D2D
communication request (A) indicating that the start of the D2D
communication is desired. The D2D communication request (A)
includes the identifier of the UE (A) 100-1 and the identifier of
the application to be used in the D2D communication. The D2D
communication request (A) further includes information on the
transmission power of the search signal and information on the
received power of the response signal.
[0103] When the D2D communication request (A) is received, the eNB
200 measures received power of the D2D communication request (A),
adds information on the measured received power to the D2D
communication request (A), and transfers the D2D communication
request (A) to the MME/S-GW 300.
[0104] In step S4, in response to the transmission of the response
signal, the UE (B) 100-2 transmits, to the eNB 200, a D2D
communication request (B) indicating that the start of the D2D
communication is desired. The D2D communication request (B)
includes the identifier of the UE (B) 100-2 and the identifier of
the application to be used in the D2D communication. The D2D
communication request (B) further includes information on the
transmission power of the response signal and information on the
received power of the search signal.
[0105] When the D2D communication request (B) is received, the eNB
200 measures received power of the D2D communication request (B),
adds information on the measured received power to the D2D
communication request (B), and transfers the D2D communication
request (B) to the MME/S-GW 300.
[0106] When the D2D communication request (A) and the D2D
communication request (B) are received, the MME/S-GW 300 determines
whether the D2D communication by the UE (A) 100-1 and the UE (B)
100-2 is possible on the basis of a distance between the UEs, a
distance between the UE and the eNB, application characteristics
and the like, which are obtained from the D2D communication request
(A) and the D2D communication request (B). For example, the
MME/S-GW 300 determines whether the D2D communication is possible
by at least one of the following first determination reference to
third determination reference.
[0107] Firstly, when the UE (B) 100-2 does not exist in the
vicinity of the UE (A) 100-1, the MME/S-GW 300 determines that the
D2D communication is not possible. This is because the D2D
communication is basically performed between neighboring UEs 100,
and interference and a battery consumption amount are increased
when the D2D communication is performed between UEs 100 remote from
each other.
[0108] For example, since it is possible to know propagation loss
by the difference between the transmission power of the search
signal included in the D2D communication request (A) and the
received power of the search signal included in the D2D
communication request (B), the MME/S-GW 300 is able to estimate a
distance between the UE (A) 100-1 and the UE (B) 100-2 on the basis
of the propagation loss. Similarly, since it is possible to know
propagation loss by the difference between the transmission power
of the response signal included in the D2D communication request
(B) and the received power of the response signal included in the
D2D communication request (A), the MME/S-GW 300 is able to estimate
the distance between the UE (A) 100-1 and the UE (B) 100-2 on the
basis of the propagation loss.
[0109] In addition, when the transmission power of the search
signal and the transmission power of the response signal are each
uniformly defined in an entire system in advance, information on
the transmission power may not be included in the D2D communication
request.
[0110] Secondly, when the eNB 200 exists in the vicinity of the UE
(A) 100-1 or the eNB 200 exists in the vicinity of the UE (B)
100-2, the MME/S-GW 300 determines that the D2D communication is
not possible. This is because interference to the eNB 200 is
increased when the D2D communication is performed in the vicinity
of the eNB 200.
[0111] For example, since it is possible to know rough propagation
loss from received power when the eNB 200 received the D2D
communication request (A), the MME/S-GW 300 is able to estimate the
distance between the UE (A) 100-1 and the eNB 200 on the basis of
the propagation loss. Similarly, since it is possible to know rough
propagation loss from received power when the eNB 200 received the
D2D communication request (B), the MME/S-GW 300 is able to estimate
the distance between the UE (B) 100-2 and the eNB 200 on the basis
of the propagation loss. In addition, in order to accurately obtain
the propagation loss, the transmission power of the D2D
communication request may be notified from the UE.
[0112] Thirdly, in the case of an application that generates
temporary traffic or in a small amount (a low load), the MME/S-GW
300 determines that the D2D communication is not possible. In other
words, only in the case of an application that generates continuous
traffic with a large capacity (a high load), the MME/S-GW 300
determines that the D2D communication is possible. This is because
a merit of the D2D communication may not be sufficiently achieved
when treating traffic temporarily or in a low load.
[0113] For example, since a streaming or video communication
application generates continuous traffic with a high load, the
MME/S-GW 300 determines that the D2D communication is possible.
Details thereof will be described later, but the D2D communication
may also be applied to the application that generates the traffic
temporarily or in a small amount (a low load).
[0114] When it is determined that the D2D communication by the UE
(A) 100-1 and the UE (B) 100-2 is possible, the MME/S-GW 300
notifies the eNB 200 of necessary information and the fact that the
D2D communication is possible, so that the D2D communication is
started under the control of the eNB 200.
[0115] According to the operation pattern 1, the D2D communication
is possible only when the UE (A) 100-1 and the UE (B) 100-2 are in
a state suitable for the D2D communication.
[0116] (3.1.2) Operation Pattern 2
[0117] The aforementioned operation pattern 1 assumes the case in
which the UE (B) always waits for the search signal. However, for
example, it is possible to assume the case of stopping waiting for
the search signal in order to reduce a battery consumption amount.
In this regard, in the operation pattern 2, it is assumed that UE
(A) is able to discover UE (B) in such a sleep state of the D2D
communication.
[0118] FIG. 9 is a sequence diagram of the search operation pattern
2 according to the present embodiment.
[0119] As illustrated in FIG. 9, in step S11, the UE (A) 100-1
transmits, to the eNB 200, a D2D communication request indicating
that the start of the D2D communication is desired. The eNB 200
transfers the D2D communication request from the UE (A) 100-1 to
the MME/S-GW 300. The D2D communication request includes the
identifier of the UE (A) 100-1 and the identifier of the
application to be used in the D2D communication. The D2D
communication request may further include an identifier of the UE
(B) 100-2 that is a communication partner, or an identifier of a
group (a D2D communication group) of the UE 100 which will perform
the D2D communication.
[0120] In step S12, the MME/S-GW 300 designates UE (B) 100-2, which
satisfies the D2D communication request from the UE (A) 100-1,
among UEs 100 existing in a camping area (or a camping cell) of the
UE (A) 100-1. Furthermore, the MME/S-GW 300 confirms the state of
the UE (B) 100-2 so as to determine whether the waiting for the
search signal is in progress or being cancelled. Hereinafter, the
following description will be given on the assumption that the UE
(B) 100-2 stops waiting for the search signal.
[0121] In step S13, the MME/S-GW 300 transmits, to the eNB 200, a
waiting start request directed to the UE (B) 100-2. The eNB 200
transfers the waiting start request from the MME/S-GW 300 to the UE
(B) 100-2.
[0122] In step S14, when the waiting start request is received, the
UE (B) 100-2 starts to wait for the search signal. Specifically,
the UE (B) 100-2 attempts the reception of the search signal at a
predetermined cycle.
[0123] After starting to wait for the search signal, when the
search signal from the UE (A) 100-1 is received (step S1), the UE
(B) 100-2 transmits a response signal for the search signal to the
UE (A) 100-1 (step S2). Subsequent operations are similar to those
of the operation pattern 1.
[0124] According to the operation pattern 2, the UE (B) 100-2 even
in the sleep state of the D2D communication can be discovered by
the UE (A) 100-1.
[0125] (3.2) Radio Resource Assignment in D2D Communication
[0126] Next, an assignment operation of a radio resource in the D2D
communication will be described. The "radio resource" indicates a
resource block (RB) that is a unit of a time-frequency resource,
that is, a frequency band. Furthermore, a modulation and coding
scheme (MCS) in radio communication may be included in the "radio
resource".
[0127] (3.2.1) Method of Assigning Radio Resource
[0128] The eNB 200 performs quasi-static radio resource assignment
for the D2D communication. In the present embodiment, the eNB 200
determines a method of assigning radio resource in the D2D
communication in response to the characteristics of an application
that is used in the D2D communication.
[0129] FIG. 10 is a flow diagram of a determination operation of
the method of assigning radio resource in the present embodiment.
Before the present flow is performed, the eNB 200 acquires an
identifier of the application, which is used in the D2D
communication, from the MME/S-GW 300. Alternatively, the eNB 200
may acquire the identifier of the application, which is used in the
D2D communication, from the UE 100 performing the D2D
communication.
[0130] As illustrated in FIG. 10, in step S21, the eNB 200
recognizes the characteristics of the application from the
identifier of the application that is used in the D2D
communication. For example, the eNB 200 holds in advance a table,
in which the identifier of the application is correlated with the
characteristics thereof, and is able to recognize the
characteristics of the application by using the table.
[0131] When traffic generated by the application used in the D2D
communication produces a low load and is temporary (for example, in
the case of a chat and the like), the eNB 200 determines to assign
a radio resource, which is commonly used in another D2D
communication, to the D2D communication in step S22. In this way,
it is possible to save the radio resource. In this case, difference
codes (spread codes) are assigned to each of various types of D2D
communication to which the same radio resource is assigned, so that
code division is possible. For example, a code 1 is assigned to a
D2D communication pair 1 and a code 2 is assigned to a D2D
communication pair 2, so that each pair is able to separate the
information of one pair from the information of the other pair.
[0132] Furthermore, when the traffic generated by the application
used in the D2D communication produces a high load and is
continuous (for example, in the case of streaming and the like),
the eNB 200 determines to periodically assign a dedicated radio
resource to the D2D communication in step S23. In this way, it is
possible to transmit a large amount of traffic in the D2D
communication.
[0133] Moreover, when the traffic generated by the application used
in the D2D communication has a high load, is continuous, and
requires low delay (for example, video communication and the like),
the eNB 200 determines assignment such that the dedicated radio
resource is repeatedly transmitted in a cyclic manner, in step S24.
In this way, it is possible to transmit a large amount of traffic
in the D2D communication and also possible to enhance the
reliability of communication. The repetitive transmission is not
limited to a scheme for repeatedly transmitting the same data a
plurality of times. For example, the repetitive transmission may
include a scheme for changing a redundant bit whenever the radio
resource is transmitted and repeatedly transmitting the radio
resource (for example, an Incremental Redundancy scheme).
[0134] In accordance with the method of assigning radio resource
according to the present embodiment, it is possible to
appropriately assign the radio resource in the D2D communication in
response to the characteristics of the application used in the D2D
communication.
[0135] (3.2.2) Radio Resource Assignment Based on Buffer State
Report
[0136] When the UE 100 simultaneously performs the cellular
communication and the D2D communication, it is preferable that the
eNB 200 is able to control radio resource assignment for the D2D
communication, separately from the cellular communication. In the
present embodiment, it is assumed that the radio resource
assignment is controlled for the D2D communication, separately from
the cellular communication.
[0137] Furthermore, in the cellular communication, there is a
scheme in which the UE 100 transmits a buffer state report (BSR) to
the eNB 200, and the eNB 200 controls the assignment of an uplink
radio resource to the UE 100 on the basis of the BSR from the UE
100, the BSR indicating the amount of data waiting for transmission
(a transmission buffer stay amount) to the eNB 200. In the present
embodiment, it is assumed that the radio resource assignment is
also controlled in the D2D communication on the basis of the
BSR.
[0138] Hereinafter, a description will be provided for an operation
for performing radio resource assignment control of the D2D
communication by employing an example in which the UE (A) 100-1
performing only the cellular communication by using a plurality of
applications switches a part of the applications to the D2D
communication.
[0139] FIG. 11 is a diagram for explaining the operation of the UE
(A) 100-1 performing only the cellular communication by using a
plurality of applications.
[0140] As illustrated in FIG. 11, the UE (A) 100-1 implements
applications 0, 1, 2, 3, . . . , and transmits traffic generated by
each application and a control signal to the eNB 200 by using a
plurality of logical channels. In the physical (PHY) layer, each
logical channel is provided with a buffer for temporarily holding
data transmitted through the logical channel.
[0141] The logical channels are grouped into a plurality of logical
channel groups (LCG). In the example of FIG. 11, there are four
LCGs of LCG 0 to LCG 3. When BSR is transmitted for each logical
channel, since overhead is increased, the BSR is defined to be
transmitted for each LCG.
[0142] The UE (A) 100-1 transmits the BSR to the eNB 200 for each
of the LCG 0 to the LCG 3. A scheduler of the eNB 200 recognizes a
transmission buffer stay amount indicated by the BSR for each of
the LCG 0 to the LCG 3, and performs uplink radio resource
assignment corresponding to the transmission buffer stay
amount.
[0143] FIG. 12 is a diagram for explaining the operation of the UE
(A) 100-1 when switching a part of the applications to the D2D
communication with the UE (B) 100-2 from the situation of FIG.
11.
[0144] When switching a part of the applications to the D2D
communication, the MME/S-GW 300 (or the eNB 200) designates an
application (here, the application 0) to be used in the D2D
communication, and notifies the UE (A) 100-1 of the designated
application 0.
[0145] The UE (A) 100-1 sets certain LCG (here, the LCG 3) to be
dedicated for the application 0. That is, the UE (A) 100-1 secures
the LCG 3 for the D2D communication, in addition to the LCG 0 to
the LCG 2 for the cellular communication.
[0146] Furthermore, the UE (A) 100-1 secures a hardware resource
for the D2D communication with respect to the LCG 3 for the D2D
communication. The hardware resource indicates a resource (a
processing resource) of the processor 160 and a resource (a memory
resource) of the memory 150.
[0147] Moreover, the UE (A) 100-1 notifies the eNB 200 of the LCG 3
for the D2D communication.
[0148] The eNB 200 assigns a radio network temporary identifier
(RNTI) for the D2D communication to the LCG 3 for the D2D
communication, which was notified from the UE (A) 100-1. The RNTI
is a UE identifier that is temporarily provided for control. For
example, the PDCCH includes RNTI of the UE 100 that is a
transmission destination, and the UE 100 determines the presence or
absence of radio resource assignment on the basis of the presence
or absence of the RNTI of the UE 100 in the PDCCH.
[0149] Hereinafter, the RNTI for the D2D communication is called
"D2D-RNTI". In this way, the eNB 200 assigns the D2D-RNTI to the UE
(A) 100-1, in addition to RNTI (C-RNTI) for the cellular
communication. As a consequence, the total two RNTIs (the C-RNTI
and the D2D-RNTI) are assigned to the UE (A) 100-1, so that initial
setting of the D2D communication is completed.
[0150] FIG. 13 is a diagram for explaining the operation of the UE
(A) 100-1 during the D2D communication.
[0151] As illustrated in FIG. 13, in step S31, the UE (A) 100-1
transmits BSR MCE (MAC Control Element) to the eNB 200 together
with transmission data (DAT) directed to the eNB 200. The BSR MCE
includes BSRs of each of the LCG 0 to the LCG 3.
[0152] In step S32, on the basis of the BSR MCE, the eNB 200
recognizes a transmission buffer stay amount indicated by the BSR
with respect to each of the LCG 0 to the LCG 3, and performs radio
resource assignment corresponding to the transmission buffer stay
amount for each of the LCG 0 to the LCG 3. Furthermore, on the
basis of the transmission buffer stay amount for the LCG 3, the eNB
200 determines a radio resource to be assigned to the D2D
communication. Then, the eNB 200 notifies the UE (A) 100-1 of the
radio resource, which is to be assigned to the D2D communication,
using the D2D-RNTI on the PDCCH.
[0153] In step S33, the UE (A) 100-1 transmits to the UE (B) 100-2
by using the radio resource assigned to the D2D communication.
[0154] In accordance with the radio resource assignment according
to the present embodiment, it is possible to control radio resource
assignment for the D2D communication, separately from the cellular
communication. Furthermore, it is also possible to control the
assignment of a radio resource in the D2D communication on the
basis of the BSR.
[0155] (3.3) Transmission Power Control of D2D Communication
[0156] As described above, when the traffic generated by the
application used in the D2D communication produces a high load and
is continuous, a dedicated radio resource is periodically assigned
to the D2D communication. The UE (A) 100-1 and the UE (B) 100-2
performing the D2D communication alternately use the periodically
assigned radio resource for transmission. Furthermore, the UE (A)
100-1 and the UE (B) 100-2 may perform repetitive transmission in
response to an error situation and the like.
[0157] FIG. 14 is a diagram for explaining transmission power
control and retransmission control in the D2D communication. In
FIG. 14, steps S41, S43, and S44 correspond to the D2D
communication and step S42 corresponds to the cellular
communication.
[0158] As illustrated in FIG. 14, in step S41, the UE (A) 100-1
transmits data 1 to the UE (B) 100-2. The UE (A) 100-1 transmits
TxPower MCE including information on transmission power of the
transmission together with the data 1. In this way, when
transmitting a radio signal to the UE (B) 100-2, the UE (A) 100-1
notifies the UE (B) 100-2 of the transmission power. Furthermore,
the UE (A) 100-1 transmits HARQ Ack/Nack MCE including information
on HARQ Ack/Nack for data 0, which was received from the UE (B)
100-2 in previous time, together with the data 1.
[0159] When the data 1 is received from the UE (A) 100-1, the UE
(B) 100-2 measures received power of the reception. Furthermore, on
the basis of the difference between the measured received power and
the transmission power indicated by the TxPower MCE transmitted
together with the data 1, the UE (B) 100-2 determines transmission
power when performing next transmission with respect to the UE (A)
100-1. For example, as the difference between the transmission
power and the received power of the data 1 from the UE (A) 100-1 is
large, since propagation loss is large, the UE (B) 100-2 determines
the transmission power when performing the next transmission with
respect to the UE (A) 100-1 to be large.
[0160] In step S42, each of the UE (A) 100-1 and the UE (B) 100-2
performs transmission of data to the eNB 200. As described above,
the UE (A) 100-1 and the UE (B) 100-2 transmit the BSR MCE at the
time of the transmission of the data to the eNB 200.
[0161] In step S43, the UE (B) 100-2 transmits data 2 to the UE (A)
100-1. The UE (B) 100-2 transmits TxPower MCE including information
on transmission power of the transmission together with the data 2.
In this way, when transmitting a radio signal to the UE (A) 100-1,
the UE (B) 100-2 notifies the UE (B) 100-2 of the transmission
power. Furthermore, the UE (B) 100-2 transmits HARQ Ack/Nack MCE
including information on HARQ Ack/Nack for the data 1, which was
received from the UE (A) 100-1 in previous time, together with the
data 2.
[0162] When the data 2 is received from the UE (B) 100-2, the UE
(A) 100-1 measures received power of the data 2. Furthermore, on
the basis of the difference between the measured received power and
the transmission power indicated by the TxPower MCE transmitted
together with the data 2, the UE (A) 100-1 determines transmission
power when performing next transmission with respect to the UE (B)
100-2.
[0163] In step S44, the UE (A) 100-1 transmits the data 3 to the UE
(B) 100-2. The UE (A) 100-1 transmits TxPower MCE including
information on transmission power of the transmission together with
the data 3. Furthermore, the UE (A) 100-1 transmits HARQ Ack/Nack
MCE including information on HARQ Ack/Nack for data 2, which was
received from the UE (B) 100-2 in previous time, together with the
data 3.
[0164] Such processes are repeated, so that the transmission power
control and the retransmission control in the D2D communication are
performed.
[0165] In addition, when the distance between the UE (A) 100-1 and
the UE (B) 100-2 is increased by the movement of the UE (A) 100-1
and/or the UE (B) 100-2, transmission power in the D2D
communication becomes large. In the present embodiment, when the
transmission power in the D2D communication exceeds maximum
transmission power, the D2D communication is controlled to be
stopped and switched to the cellular communication.
[0166] FIG. 15 is a sequence diagram when the transmission power in
the D2D communication exceeds the maximum transmission power.
[0167] As illustrated in FIG. 15, in step S51, the eNB 200
transmits, on a broadcast channel (BCCH), maximum power information
indicating maximum transmission power permitted in the D2D
communication. Specifically, the eNB 200 puts the maximum power
information into a master information block (MIB) or a system
information block (SIB) and transmits the MIB or the SIB. When
starting the D2D communication, the UE (A) 100-1 and/or the UE (B)
100-2 acquires and stores the maximum power information from the
eNB 200.
[0168] In step S52, the UE (A) 100-1 and the UE (B) 100-2 perform
the D2D communication. Hereinafter, the following description will
be given on the assumption that the UE (A) 100-1 detects that the
transmission power in the D2D communication exceeds the maximum
transmission power.
[0169] In step S53, the UE (A) 100-1 notifies the eNB 200 of the
fact that the transmission power in the D2D communication exceeds
the maximum transmission power. In other words, the UE (A) 100-1
requests the eNB 200 to switch the D2D communication to the
cellular communication.
[0170] In step S54, the eNB 200 instructs the UE (A) 100-1 and the
UE (B) 100-2 to switch the D2D communication to the cellular
communication, and performs the assignment of a radio resource for
the cellular communication.
[0171] In steps S55 and S56, the UE (A) 100-1 and the UE (B) 100-2
switch the D2D communication to the cellular communication.
[0172] In accordance with the transmission power control according
to the present embodiment, it is possible to appropriately control
the transmission power in the D2D communication.
[0173] (3.4) Interference Avoidance Operation of D2D
Communication
[0174] (3.4.1) Overview of Operation
[0175] In the present embodiment, when the D2D communication
receives interference from the cellular communication or another
D2D communication, the interference is avoided by changing radio
resource assignment.
[0176] FIG. 16 and FIG. 17 are diagrams for explaining an
interference avoidance operation according to the present
embodiment. In FIG. 16 and FIG. 17, a pair of UE (1A) 100-1 and UE
(1B) 100-2 performs the D2D communication and a pair of UE (2A)
100-3 and UE (2B) 100-4 also performs the D2D communication.
Furthermore, it is assumed that radio resources used in each D2D
communication are equal to each other and receive the influence of
interference from each other.
[0177] As illustrated in FIG. 16, when a reception failure is
detected, the UE (1A) 100-1 transmits a failure notification
related to the reception failure during the D2D communication, to
the eNB 200. The reception failure indicates failure of reception
at a reception timing (specifically, it is not possible to decode
received data). The failure notification includes the identifier of
the UE (1A) 100-1 and information indicating that the D2D
communication is being performed. In addition, when it is possible
to receive and decode an interference wave from the other D2D
communication pair that is a cause of the reception failure, the UE
(A) 100-1 may determine that the other D2D communication pair is an
interference source and include information on the other D2D
communication pair, in the failure notification.
[0178] Furthermore, similarly, when reception failure is detected,
the UE (2A) 100-3 also transmits failure notification related to
the reception failure during the D2D communication to the eNB 200.
The failure notification includes the identifier of the UE (2A)
100-3 and information indicating that the D2D communication is
being performed. In addition, when it is possible to receive and
decode an interference wave from the other D2D communication pair
that is a cause of the reception failure, the UE (2A) 100-3 may
determine that the other D2D communication pair is an interference
source and include information on the other D2D communication pair,
in the failure notification.
[0179] When receiving each failure notification from the D2D
communication pair including the UE (1A) 100-1 and the UE (1B)
100-2 and the D2D communication pair including the UE (2A) 100-3
and the UE (2B) 100-4, the eNB 200 determines whether each D2D
communication pair uses the same radio resource in the D2D
communication.
[0180] As illustrated in FIG. 17, when it is determined that each
D2D communication pair uses the same radio resource in the D2D
communication, the eNB 200 determines that each D2D communication
pair receives the influence of interference from each other and
changes the assignment of the radio resource of one D2D
communication pair. For example, the eNB 200 reassigns a different
radio resource to the D2D communication pair including the UE (1A)
100-1 and the UE (1B) 100-2. In this way, the interference of the
D2D communication is avoided.
[0181] (3.4.2) Detailed Operation
[0182] As described above, the LTE system according to the present
embodiment supports the D2D communication in which radio
communication is directly performed between the UE (A) 100-1 and
the UE (B) 100-2 in the frequency and the time (the radio resource)
assigned from the eNB 200.
[0183] When it is assumed that the UE (A) 100-1 is a data
transmission side and the UE (B) 100-2 is a data reception side, if
the UE (B) 100-2 does not receive data from the UE (A) 100-1 in a
time (at a reception timing) in which the data is to be received
from the UE (A) 100-1, the UE (B) 100-2 transmits failure
notification indicating reception failure in the D2D communication
to the eNB 200.
[0184] In this way, the eNB 200 is able to recognize a generation
status of the reception failure in the D2D communication, thereby
taking measures to solve the reception failure. Consequently, it is
possible to appropriately control the D2D communication in
consideration of the generation status of the reception failure in
the D2D communication.
[0185] However, according to such a method, when there is no data
to be transmitted from the UE (A) 100-1 to the UE (B) 100-2, that
is, when a transmission buffer for the D2D communication in the UE
(A) 100-1 is empty, since the UE (B) 100-2 is not able to receive
the data from the UE (A) 100-1, determination that reception
failure has occurred is erroneously made.
[0186] As a consequence, even though reception failure
(interference) does not actually occur, the eNB 200 performs an
unnecessary process such as changing the assignment of a radio
resource.
[0187] Hereinafter, an operation (the operation patterns 1 and 2)
for avoiding such a failure will be described.
[0188] (3.4.2.1) Operation Pattern 1
[0189] FIG. 18 is an operation flow diagram of the UE (A) 100-1 in
the operation pattern 1. The UE (A) 100-1 repeats the present
flow.
[0190] As illustrated in FIG. 18, in step S611, the UE (A) 100-1
determines whether a current time is a time in which data is to be
transmitted to the UE (B) 100-2.
[0191] When a result of the determination in step S611 is "YES",
the UE (A) 100-1 determines whether the transmission buffer thereof
for the D2D communication is empty in step S612. Note that the
transmission buffer for the D2D communication is a buffer that
temporarily stores data (user data) to be newly transmitted in the
D2D communication. Thus, when the transmission buffer for the D2D
communication is empty, it indicates that there is no data to be
newly transmitted in the D2D communication.
[0192] When a result of the determination in step S612 is "YES",
the UE (A) 100-1 determines whether a passage time after data is
finally transmitted to the UE (B) 100-2 is smaller than a threshold
value in step S613.
[0193] When a result of the determination in step S613 is "YES",
the UE (A) 100-1 repeatedly transmits the data finally transmitted
to the UE (B) 100-2 in step S614. In this way, it is possible to
prevent erroneous determination in the UE (B) 100-2, and to improve
the reliability of communication by allowing the UE (B) 100-2 to
repeatedly receive the same data. For example, the UE (B) 100-2
synthesizes the same data repeatedly received, thereby enhancing a
decoding success rate of the data.
[0194] Meanwhile, when the result of the determination in step S613
is "NO", the UE (A) 100-1 transmits dummy data to the UE (B) 100-2
in step S615. Furthermore, the dummy data, for example, indicates
data, other than user data, such as a measurement result of a radio
state or 0 padding. When the result of the determination in step
S613 is "NO", that is, when a long time passes after the data is
finally transmitted to the UE (B) 100-2, it is meaningless even if
the repetitive transmission is performed after that. In this
regard, instead of the repetitive transmission, the dummy data is
transmitted, so that it is possible to prevent meaningless
repetitive transmission.
[0195] (3.4.2.2) Operation Pattern 2
[0196] FIG. 19 is an operation flow diagram of the UE (A) 100-1 in
the operation pattern 2. The UE (A) 100-1 repeats the present
flow.
[0197] As illustrated in FIG. 19, in step S621, the UE (A) 100-1
determines whether a current time is a time in which data is to be
transmitted to the UE (B) 100-2.
[0198] When a result of the determination in step S621 is "YES",
the UE (A) 100-1 determines whether the transmission buffer thereof
for the D2D communication is empty in step S622.
[0199] When a result of the determination in step S622 is "YES",
the UE (A) 100-1 transmits, to the eNB 200, data notification
indicating that there is no data to be transmitted to the UE (B)
100-2 (that is, notification indicating that the D2D transmission
buffer is empty), in step S623. Note that, as the data
notification, the aforementioned BSR for the D2D communication may
be used.
[0200] FIG. 20 is an operation sequence diagram in the operation
pattern 2.
[0201] As illustrated in FIG. 20, in step S631, the UE (A) 100-1
transmits data to the UE (B) 100-2 in a time (at a transmission
timing) in which the data is to be transmitted to the UE (B)
100-2.
[0202] In step S632, the transmission buffer of the UE (A) 100-1
for the D2D communication becomes empty.
[0203] In step S633, the UE (A) 100-1 transmits, to the eNB 200,
data notification indicating that there is no data to be
transmitted to the UE (B) 100-2 (that is, notification indicating
that the D2D transmission buffer is empty).
[0204] In addition, differently from the operation pattern 1, in
the operation pattern 2, when there is no data to be transmitted to
the UE (B) 100-2, the UE (A) 100-1 transmits no data to the UE (B)
100-2.
[0205] In step S634, the UE (B) 100-2 determines that reception
failure has occurred in the D2D communication because no data is
received from the UE (A) 100-1 in a time (at a reception timing) in
which data is received from the UE (A) 100-1.
[0206] In step S635, the UE (B) 100-2 transmits failure
notification indicating reception failure in the D2D communication
to the eNB 200.
[0207] In step S636, the eNB 200 regards that the failure
notification from the UE (B) 100-2 is not caused by reception
failure because the failure notification is received from the UE
(B) 100-2 but the data notification is received from the UE (A)
100-1 in step S633. In other words, the eNB 200 ignores the failure
notification from the UE (B) 100-2.
[0208] As described above, after the eNB 200 receives the data
notification from the UE (A) 100-1, when the eNB 200 receives the
failure notification from the UE (B) 100-2, the eNB 200 ignores the
failure notification from the UE (B) 100-2. In this way, it is
possible to prevent determination that reception failure has
occurred from being erroneously made in the eNB 200.
Other Embodiments
[0209] It should not be understood that those descriptions and
drawings constituting a part of the present disclosure limit the
present invention. Further, various substitutions, examples, or
operational techniques shall be apparent to a person skilled in the
art on the basis of this disclosure.
[0210] In the aforementioned embodiment, an entity determining
whether the D2D communication is possible is the MME/S-GW 300.
However, the eNB 200 may determine whether the D2D communication is
possible.
[0211] In the aforementioned embodiment, an entity determining the
method of assigning radio resource is the eNB 200. However, the
MME/S-GW 300 may determine the method of assigning radio resource
and notify the eNB 200 of a result of the determination.
Furthermore, the aforementioned embodiment has described an example
of determining the method of assigning radio resource on the basis
of the identifier of an application. However, instead of the
identifier of the application, an identifier of communication
quality (that is, QoS) required for the application may be used.
Such an identifier of the QoS is called QCI (QoS Class
Identifier).
[0212] In the aforementioned embodiment, the eNB 200 transmits, on
the broadcast channel (BCCH), the maximum power information
indicating the maximum transmission power permitted in the D2D
communication. However, the maximum power information may be
individually transmitted to the UE 100. In this case, it is
preferable that the eNB 200 determines the maximum transmission
power permitted in the D2D communication in response to propagation
loss between the eNB 200 and the UE 100. For example, as the
propagation loss between the eNB 200 and the UE 100 is small, the
eNB 200 determines the maximum transmission power permitted in the
D2D communication to be small.
[0213] In addition, the entire contents of U.S. Provisional
Application No. 61/656,194 (filed on Jun. 6, 2012) and U.S.
Provisional Application No. 61/693,993 (filed on Aug. 28, 2012) are
incorporated in the present specification by reference.
INDUSTRIAL APPLICABILITY
[0214] As described above, the present invention is able to a
ppropriately control the D2D communication, and thus is available
for a radio communication field such as cellular mobile
communication.
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