U.S. patent application number 14/649062 was filed with the patent office on 2015-12-03 for method for obtaining synchronization for device-to-device communication outside of coverage area in a wireless communication system and apparatus for same.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Hanbyul SEO.
Application Number | 20150351058 14/649062 |
Document ID | / |
Family ID | 50883701 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150351058 |
Kind Code |
A1 |
SEO; Hanbyul |
December 3, 2015 |
METHOD FOR OBTAINING SYNCHRONIZATION FOR DEVICE-TO-DEVICE
COMMUNICATION OUTSIDE OF COVERAGE AREA IN A WIRELESS COMMUNICATION
SYSTEM AND APPARATUS FOR SAME
Abstract
Disclosed in the present invention is a method for performing
device-to-device communication between units of user equipment
outside of a coverage area of a base station in a wireless
communication system. More specifically, the method comprises the
steps of: dividing into a plurality of candidate sections a
specific time unit for the device-to-device communication;
detecting a reference signal, which is transmitted from a second
user equipment from among the units user equipment, from one
section of the candidate sections that is not the last section;
obtaining synchronization for device-to-device communication with
the second user equipment based on the reference signal; and
transmitting a predetermined authorization signal from the last
section of the candidate sections or from a time unit after a
specific time unit.
Inventors: |
SEO; Hanbyul; (Anyang-si,
Gyeonggi-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
50883701 |
Appl. No.: |
14/649062 |
Filed: |
December 5, 2013 |
PCT Filed: |
December 5, 2013 |
PCT NO: |
PCT/KR2013/011212 |
371 Date: |
June 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61735049 |
Dec 9, 2012 |
|
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61767805 |
Feb 22, 2013 |
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61769722 |
Feb 26, 2013 |
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Current U.S.
Class: |
370/350 |
Current CPC
Class: |
H04W 56/0025 20130101;
H04W 56/0045 20130101; H04W 88/02 20130101; H04L 5/0048 20130101;
H04W 88/08 20130101; H04W 88/04 20130101; H04W 76/14 20180201; H04W
72/14 20130101; H04W 56/002 20130101; H04W 4/08 20130101; H04W
76/00 20130101 |
International
Class: |
H04W 56/00 20060101
H04W056/00; H04L 5/00 20060101 H04L005/00; H04W 72/14 20060101
H04W072/14; H04W 76/02 20060101 H04W076/02 |
Claims
1.-12. (canceled)
13. A method for transmitting synchronization signals for a
Device-to-Device (D2D) link at a user equipment (UE) located
outside a coverage of a base station in a wireless communication
system, the method comprising; receiving a first synchronization
signal for the D2D link from a first UE located within the coverage
of the base station; generating a second synchronization signal for
the D2D link using the first synchronization signal; and
transmitting the second synchronization signal for the D2D link,
wherein the first and second synchronization signals are generated
based on a same signature, wherein the first synchronization signal
includes a first indicator indicating that the first
synchronization signal is transmitted by an instruction of the base
station.
14. The method of claim 13, wherein the second synchronization
signal includes a second indicator indicating that the second
synchronization signal is a grant signal corresponding to the first
synchronization signal.
15. The method of claim 13, wherein, if a second UE located outside
the coverage of the base station receives the second
synchronization signal, the second UE obtains a synchronization
with a base station using the second synchronization signal.
16. The method of claim 13, wherein the first and second
synchronization signals are transmitted using different time
resources.
17. The method of claim 13, wherein the first and second
synchronization signals include information on a bandwidth for the
D2D link.
18. A user equipment (UE) in a wireless communication system, the
UE comprising: a Radio Frequency (RF) module to transmit and
receive signal with a base station or another UE; and a processor
to processing the signal, wherein, when the UE is located outside a
coverage of the base station, the processor controls the RF module
to receive a first synchronization signal for a Device-to-Device
(D2D) link from a first UE located within the coverage of the base
station and to transmit a second synchronization signal for the D2D
link generated by using the first synchronization signal, wherein
the first and second synchronization signals are generated based on
a same signature, wherein the first synchronization signal includes
a first indicator indicating that the first synchronization signal
is transmitted by an instruction of the base station.
19. The UE of claim 18, wherein the second synchronization signal
includes a second indicator indicating that the second
synchronization signal is a grant signal corresponding to the first
synchronization signal.
20. The UE of claim 18, wherein, if a second UE located outside the
coverage of the base station receives the second synchronization
signal, the second UE obtains a synchronization with a base station
using the second synchronization signal.
21. The UE of claim 18, wherein the first and second
synchronization signals are transmitted using different time
resources.
22. The UE of claim 18, wherein the first and second
synchronization signals include information on a bandwidth for the
D2D link.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more particularly to a method and apparatus for
acquiring synchronization for Device-to-Device (D2D) communication
at the outside of a coverage region in a wireless communication
system.
BACKGROUND ART
[0002] 3GPP LTE (3rd generation partnership project long term
evolution hereinafter abbreviated LTE) communication system is
schematically explained as an example of a wireless communication
system to which the present invention is applicable.
[0003] FIG. 1 is a schematic diagram of E-UMTS network structure as
one example of a wireless communication system. E-UMTS (evolved
universal mobile telecommunications system) is a system evolved
from a conventional UMTS (universal mobile telecommunications
system). Currently, basic standardization works for the E-UMTS are
in progress by 3GPP. E-UMTS is called LTE system in general.
Detailed contents for the technical specifications of UMTS and
E-UMTS refers to release 7 and release 8 of "3rd generation
partnership project; technical specification group radio access
network", respectively.
[0004] Referring to FIG. 1, E-UMTS includes a user equipment (UE),
an eNode B (eNB), and an access gateway (hereinafter abbreviated
AG) connected to an external network in a manner of being situated
at the end of a network (E-UTRAN). The eNode B may be able to
simultaneously transmit multi data streams for a broadcast service,
a multicast service and/or a unicast service.
[0005] One eNode B contains at least one cell. The cell provides a
downlink transmission service or an uplink transmission service to
a plurality of user equipments by being set to one of 1.25 MHz, 2.5
MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz of bandwidths. Different
cells can be configured to provide corresponding bandwidths,
respectively. An eNode B controls data transmissions/receptions
to/from a plurality of the user equipments. For a downlink
(hereinafter abbreviated DL) data, the eNode B informs a
corresponding user equipment of time/frequency region on which data
is transmitted, coding, data size, HARQ (hybrid automatic repeat
and request) related information and the like by transmitting DL
scheduling information. And, for an uplink (hereinafter abbreviated
UL) data, the eNode B informs a corresponding user equipment of
time/frequency region usable by the corresponding user equipment,
coding, data size, HARQ-related information and the like by
transmitting UL scheduling information to the corresponding user
equipment. Interfaces for user-traffic transmission or control
traffic transmission may be used between eNode Bs. A core network
(CN) consists of an AG (access gateway) and a network node for user
registration of a user equipment and the like. The AG manages a
mobility of the user equipment by a unit of TA (tracking area)
consisting of a plurality of cells.
[0006] Wireless communication technologies have been developed up
to LTE based on WCDMA. Yet, the ongoing demands and expectations of
users and service providers are consistently increasing. Moreover,
since different kinds of radio access technologies are continuously
developed, a new technological evolution is required to have a
future competitiveness. Cost reduction per bit, service
availability increase, flexible frequency band use, simple
structure/open interface and reasonable power consumption of user
equipment and the like are required for the future
competitiveness.
DISCLOSURE
Technical Problem
[0007] An object of the present invention is to provide a method
and apparatus for acquiring synchronization for Device-to-Device
(D2D) communication at the outside of a coverage region in a
wireless communication system.
Technical Solution
[0008] The objects of the present invention can be achieved by
providing a method for performing Device-to-Device (D2D) direct
communication by a first user equipment (UE) from among a plurality
of UEs located outside of a base station (BS) coverage in a
wireless communication system including: dividing a specific time
unit for the D2D direct communication into a plurality of candidate
sections; detecting a reference signal (RS) received from a second
UE from among the plurality of UEs in one section other than a last
section from among the candidate sections; acquiring
synchronization for the D2D direct communication with the second
UE, on the basis of the reference signal (RS); and transmitting a
predefined validation signal in the last section from among the
candidate sections or in a next time unit of the specific time
unit.
[0009] The method may further include: receiving configuration
information configured to perform direct communication between the
second UE and a user equipment (UE), wherein the configuration
information is contained in the reference signal (RS) or is
received during a predetermined time located after the specific
time unit through a resource in which the reference signal (RS) is
detected.
[0010] The method may further include: after lapse of a
predetermined time after acquisition of the synchronization,
detecting the reference signal (RS) in one section other than a
last section from among the candidate sections, and thus
re-acquiring the synchronization.
[0011] In accordance with another aspect of the present invention,
a user equipment (UE) device for performing Device-to-Device (D2D)
direct communication in a wireless communication system includes: a
radio frequency (RF) module configured to transmit/receive a signal
to/from a base station (BS) or counterpart user equipment (UE)
devices of the D2D direct communication; a processor configured to
process the signal, wherein the processor controls the RF module in
such a manner that it divides a specific time unit for the D2D
direct communication into a plurality of candidate sections,
detects a reference signal (RS) received from a specific UE device
from among the counterpart UE devices in one section other than a
last section from among the candidate sections, acquires
synchronization for the D2D direct communication with the specific
UE device on the basis of the reference signal (RS), and transmits
a predefined validation signal in the last section from among the
candidate sections or in a next time unit of the specific time
unit.
[0012] The RF module may receive configuration information
configured to perform direct communication between the second UE
and a user equipment (UE), wherein the configuration information is
contained in the reference signal (RS) or is received during a
predetermined time located after the specific time unit through a
resource in which the reference signal (RS) is detected.
[0013] After lapse of a predetermined time after acquisition of the
synchronization, the processor may detect the reference signal (RS)
in one section other than a last section from among the candidate
sections, and thus re-acquire the synchronization.
[0014] The position of a frequency resource needed for reception of
the reference signal (RS) or a signature of the detected reference
signal (RS) may be determined on the basis of an index of a
candidate section for detecting the reference signal (RS). The
predefined validation signal may be identical to the detected
reference signal (RS). If the detected reference signal (RS) is a
propagation signal of a reference signal (RS) that is transmitted
either from another UE to the second UE or from the base station
(BS) to the second UE, the detected reference signal (RS) may
include an identifier (ID) for indicating that the reference signal
(RS) is the propagation signal.
Advantageous Effects
[0015] According to exemplary embodiments of the present invention,
the method and apparatus for acquiring synchronization can more
efficiently acquire synchronization for Device-to-Device (D2D)
communication at the outside of a coverage region in a wireless
communication system.
[0016] It will be appreciated by persons skilled in the art that
that the effects that can be achieved through the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description.
DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a diagram showing a network structure of an
Evolved Universal Mobile Telecommunications System (E-UMTS) as an
example of a wireless communication system.
[0018] FIG. 2 is a diagram showing a control plane and a user plane
of a radio interface protocol architecture between a User Equipment
(UE) and an Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) based on a 3rd Generation Partnership Project (3GPP)
radio access network standard.
[0019] FIG. 3 is a diagram showing physical channels used in a 3GPP
system and a general signal transmission method using the same.
[0020] FIG. 4 is a diagram showing the structure of a downlink
radio frame used in a Long Term Evolution (LTE) system.
[0021] FIG. 5 is a diagram showing the structure of an uplink
subframe used in an LTE system.
[0022] FIG. 6 is a diagram illustrating the concept of
device-to-device (D2D) communication.
[0023] FIG. 7 illustrates classification of subframes for D2D
communication and eNB communication.
[0024] FIG. 8 illustrates a method for transmitting a subframe
reference signal (RS) according to a first embodiment of the
present invention.
[0025] FIG. 9 illustrates the positions of subframe reference
signal (RS) transmission candidates from the viewpoint of one UE
according to a first embodiment of the present invention.
[0026] FIG. 10 illustrates reception of a subframe reference signal
(RS) and transmission of a validation signal according to a first
embodiment of the present invention.
[0027] FIG. 11 is a conceptual diagram illustrating an exemplary
case of receiving a plurality of overlapped subframe reference
signals (RSs) according to a first embodiment of the present
invention.
[0028] FIG. 12 is a conceptual diagram illustrating that a boundary
of a downlink subframe and a boundary of an uplink subframe are
changed according to a third embodiment of the present
invention.
[0029] FIG. 13 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) using a boundary of a downlink subframe according to a third
embodiment of the present invention.
[0030] FIG. 14 is a conceptual diagram illustrating another method
for determining a transmission (Tx) time of a subframe reference
signal (RS) using a boundary of a downlink subframe according to a
third embodiment of the present invention.
[0031] FIG. 15 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) using a boundary of an uplink subframe according to a third
embodiment of the present invention.
[0032] FIG. 16 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) at a time between a boundary of an uplink subframe and a
boundary of a downlink subframe according to a third embodiment of
the present invention.
[0033] FIG. 17 is a conceptual diagram illustrating a method for
propagating boundary information of a subframe used in eNB to UEs
located outside of a coverage region according to a fourth
embodiment of the present invention.
[0034] FIG. 18 is a block diagram of a communication apparatus
according to an embodiment of the present invention.
BEST MODE
[0035] In the following description, compositions of the present
invention, effects and other characteristics of the present
invention can be easily understood by the embodiments of the
present invention explained with reference to the accompanying
drawings. Embodiments explained in the following description are
examples of the technological features of the present invention
applied to 3GPP system.
[0036] In this specification, the embodiments of the present
invention are explained using an LTE system and an LTE-A system,
which is exemplary only. The embodiments of the present invention
are applicable to various communication systems corresponding to
the above mentioned definition. In particular, although the
embodiments of the present invention are described in the present
specification on the basis of FDD, this is exemplary only. The
embodiments of the present invention may be easily modified and
applied to H-FDD or TDD.
[0037] FIG. 2 is a diagram for structures of control and user
planes of radio interface protocol between a 3GPP radio access
network standard-based user equipment and E-UTRAN. The control
plane means a path on which control messages used by a user
equipment (UE) and a network to manage a call are transmitted. The
user plane means a path on which such a data generated in an
application layer as audio data, internet packet data, and the like
are transmitted.
[0038] A physical layer, which is a 1st layer, provides higher
layers with an information transfer service using a physical
channel. The physical layer is connected to a medium access control
layer situated above via a transport channel (trans antenna port
channel). Data moves between the medium access control layer and
the physical layer on the transport channel. Data moves between a
physical layer of a transmitting side and a physical layer of a
receiving side on the physical channel. The physical channel
utilizes time and frequency as radio resources. Specifically, the
physical layer is modulated by OFDMA (orthogonal frequency division
multiple access) scheme in DL and the physical layer is modulated
by SC-FDMA (single carrier frequency division multiple access)
scheme in UL.
[0039] Medium access control (hereinafter abbreviated MAC) layer of
a 2nd layer provides a service to a radio link control (hereinafter
abbreviated RLC) layer, which is a higher layer, on a logical
channel. The RLC layer of the 2nd layer supports a reliable data
transmission. The function of the RLC layer may be implemented by a
function block within the MAC. PDCP (packet data convergence
protocol) layer of the 2nd layer performs a header compression
function to reduce unnecessary control information, thereby
efficiently transmitting such IP packets as IPv4 packets and IPv6
packets in a narrow band of a radio interface.
[0040] Radio resource control (hereinafter abbreviated RRC) layer
situated in the lowest location of a 3rd layer is defined on a
control plane only. The RRC layer is responsible for control of
logical channels, transport channels and physical channels in
association with a configuration, a re-configuration and a release
of radio bearers (hereinafter abbreviated RBs). The RB indicates a
service provided by the 2nd layer for a data delivery between the
user equipment and the network. To this end, the RRC layer of the
user equipment and the RRC layer of the network exchange a RRC
message with each other. In case that there is an RRC connection
(RRC connected) between the user equipment and the RRC layer of the
network, the user equipment lies in the state of RRC connected
(connected mode). Otherwise, the user equipment lies in the state
of RRC idle (idle mode). A non-access stratum (NAS) layer situated
at the top of the RRC layer performs such a function as a session
management, a mobility management and the like.
[0041] A single cell consisting of an eNode B (eNB) is set to one
of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz of
bandwidths and then provides a downlink or uplink transmission
service to a plurality of user equipments. Different cells can be
configured to provide corresponding bandwidths, respectively.
[0042] DL transport channels for transmitting data from a network
to a user equipment include a BCH (broadcast channel) for
transmitting a system information, a PCH (paging channel) for
transmitting a paging message, a downlink SCH (shared channel) for
transmitting a user traffic or a control message and the like. DL
multicast/broadcast service traffic or a control message may be
transmitted on the DL SCH or a separate DL MCH (multicast channel).
Meanwhile, UL transport channels for transmitting data from a user
equipment to a network include a RACH (random access channel) for
transmitting an initial control message, an uplink SCH (shared
channel) for transmitting a user traffic or a control message. A
logical channel, which is situated above a transport channel and
mapped to the transport channel, includes a BCCH (broadcast
channel), a PCCH (paging control channel), a CCCH (common control
channel), a MCCH (multicast control channel), a MTCH (multicast
traffic channel) and the like.
[0043] FIG. 3 is a diagram for explaining physical channels used
for 3GPP system and a general signal transmission method using the
physical channels.
[0044] If a power of a user equipment is turned on or the user
equipment enters a new cell, the user equipment may perform an
initial cell search job for matching synchronization with an eNode
B and the like [S301]. To this end, the user equipment may receive
a primary synchronization channel (P-SCH) and a secondary
synchronization channel (S-SCH) from the eNode B, may be
synchronized with the eNode B and may then obtain information such
as a cell ID and the like. Subsequently, the user equipment may
receive a physical broadcast channel from the eNode B and may be
then able to obtain intra-cell broadcast information. Meanwhile,
the user equipment may receive a downlink reference signal (DL RS)
in the initial cell search step and may be then able to check a DL
channel state.
[0045] Having completed the initial cell search, the user equipment
may receive a physical downlink shared control channel (PDSCH)
according to a physical downlink control channel (PDCCH) and an
information carried on the physical downlink control channel
(PDCCH). The user equipment may be then able to obtain detailed
system information [S302].
[0046] Meanwhile, if a user equipment initially accesses an eNode B
or does not have a radio resource for transmitting a signal, the
user equipment may be able to perform a random access procedure to
complete the access to the eNode B [S303 to S306]. To this end, the
user equipment may transmit a specific sequence as a preamble on a
physical random access channel (PRACH) [S303/S305] and may be then
able to receive a response message on PDCCH and the corresponding
PDSCH in response to the preamble [S304/S306]. In case of a
contention based random access procedure (RACH), it may be able to
additionally perform a contention resolution procedure.
[0047] Having performed the above mentioned procedures, the user
equipment may be able to perform a PDCCH/PDSCH reception [S307] and
a PUSCH/PUCCH (physical uplink shared channel/physical uplink
control channel) transmission [S308] as a general uplink/downlink
signal transmission procedure. In particular, the user equipment
receives a DCI (downlink control information) on the PDCCH. In this
case, the DCI contains such a control information as an information
on resource allocation to the user equipment. The format of the DCI
varies in accordance with its purpose.
[0048] Meanwhile, control information transmitted to an eNode B
from a user equipment via UL or the control information received by
the user equipment from the eNode B includes downlink/uplink
ACK/NACK signals, CQI (Channel Quality Indicator), PMI (Precoding
Matrix Index), RI (Rank Indicator) and the like. In case of 3GPP
LTE system, the user equipment may be able to transmit the
aforementioned control information such as CQI/PMI/RI and the like
on PUSCH and/or PUCCH.
[0049] FIG. 4 illustrates exemplary control channels included in a
control region of a subframe in a DL radio frame.
[0050] Referring to FIG. 4, a subframe includes 14 OFDM symbols.
The first one to three OFDM symbols of a subframe are used for a
control region and the other 13 to 11 OFDM symbols are used for a
data region according to a subframe configuration. In FIG. 5,
reference characters R1 to R4 denote RSs or pilot signals for
antenna 0 to antenna 3. RSs are allocated in a predetermined
pattern in a subframe irrespective of the control region and the
data region. A control channel is allocated to non-RS resources in
the control region and a traffic channel is also allocated to
non-RS resources in the data region. Control channels allocated to
the control region include a Physical Control Format Indicator
Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH),
a Physical Downlink Control Channel (PDCCH), etc.
[0051] The PCFICH is a physical control format indicator channel
carrying information about the number of OFDM symbols used for
PDCCHs in each subframe. The PCFICH is located in the first OFDM
symbol of a subframe and configured with priority over the PHICH
and the PDCCH. The PCFICH includes 4 Resource Element Groups
(REGs), each REG being distributed to the control region based on a
cell Identifier (ID). One REG includes 4 Resource Elements (REs).
An RE is a minimum physical resource defined by one subcarrier by
one OFDM symbol. The PCFICH is set to 1 to 3 or 2 to 4 according to
a bandwidth. The PCFICH is modulated in Quadrature Phase Shift
Keying (QPSK).
[0052] The PHICH is a physical Hybrid-Automatic Repeat and request
(HARQ) indicator channel carrying an HARQ ACK/NACK for a UL
transmission. That is, the PHICH is a channel that delivers DL
ACK/NACK information for UL HARQ. The PHICH includes one REG and is
scrambled cell-specifically. An ACK/NACK is indicated in one bit
and modulated in Binary Phase Shift Keying (BPSK). The modulated
ACK/NACK is spread with a Spreading Factor (SF) of 2 or 4. A
plurality of PHICHs mapped to the same resources form a PHICH
group. The number of PHICHs multiplexed into a PHICH group is
determined according to the number of spreading codes. A PHICH
(group) is repeated three times to obtain a diversity gain in the
frequency domain and/or the time domain.
[0053] The PDCCH is a physical DL control channel allocated to the
first n OFDM symbols of a subframe. Herein, n is 1 or a larger
integer indicated by the PCFICH. The PDCCH occupies one or more
CCEs. The PDCCH carries resource allocation information about
transport channels, PCH and DL-SCH, a UL scheduling grant, and HARQ
information to each UE or UE group. The PCH and the DL-SCH are
transmitted on a PDSCH. Therefore, an eNB and a UE transmit and
receive data usually on the PDSCH, except for specific control
information or specific service data.
[0054] Information indicating one or more UEs to receive PDSCH data
and information indicating how the UEs are supposed to receive and
decode the PDSCH data are delivered on a PDCCH. For example, on the
assumption that the Cyclic Redundancy Check (CRC) of a specific
PDCCH is masked by Radio Network Temporary Identity (RNTI) "A" and
information about data transmitted in radio resources (e.g. at a
frequency position) "B" based on transport format information (e.g.
a transport block size, a modulation scheme, coding information,
etc.) "C" is transmitted in a specific subframe, a UE within a cell
monitors, that is, blind-decodes a PDCCH using its RNTI information
in a search space. If one or more UEs have RNTI "A", these UEs
receive the PDCCH and receive a PDSCH indicated by "B" and "C"
based on information of the received PDCCH.
[0055] A basic resource unit of a DL control channel is an REG. The
REG includes four contiguous REs except for REs carrying RSs. A
PCFICH and a PHICH include 4 REGs and 3 REGs, respectively. A PDCCH
is configured in units of a Control Channel Element (CCE), each CCE
including 9 REGs.
[0056] FIG. 5 illustrates a structure of a UL subframe in the LTE
system.
[0057] Referring to FIG. 5, a UL subframe may be divided into a
control region and a data region. A Physical Uplink Control Channel
(PUCCH) including Uplink Control Information (UCI) is allocated to
the control region and a Physical uplink Shared Channel (PUSCH)
including user data is allocated to the data region. The middle of
the subframe is allocated to the PUSCH, while both sides of the
data region in the frequency domain are allocated to the PUCCH.
Control information transmitted on the PUCCH may include an HARQ
ACK/NACK, a CQI representing a downlink channel state, an RI for
MIMO, a Scheduling Request (SR) requesting UL resource allocation.
A PUCCH for one UE occupies one RB in each slot of a subframe. That
is, the two RBs allocated to the PUCCH are frequency-hopped over
the slot boundary of the subframe. Particularly, PUCCHs with m=0,
m=1, m=2, and m=3 are allocated to a subframe in FIG. 5.
[0058] FIG. 6 is a diagram illustrating the concept of
device-to-device (D2D) communication.
[0059] Referring to FIG. 6, UE1 and UE2 may perform D2D direct
communication therebetween, and UE3 and UE4 may also perform D2D
direct communication therebetween. The eNB may control the position
of time/frequency resources, Tx power, etc. for UE-to-UE direct
communication through an appropriate control signal. However, if
UEs are located at the outside of an eNB coverage, UE-to-UE direct
communication may be achieved without using the eNB control signal.
For convenience of description, UE-to-UE direct communication will
hereinafter be referred to as D2D (Device-to-Device)
communication.
[0060] UE located in the eNB coverage must communicate with the eNB
simultaneously while performing D2D communication. One method for
this purpose is to classify all subframes into subframes for eNB
communication and subframes for D2D communication. FIG. 7
illustrates classification of subframes for D2D communication and
eNB communication.
[0061] Referring to FIG. 7, a UE configured to perform D2D
communication using an uplink band of an FDD system transmits an
uplink signal to the eNB at a first subframe shown in FIG. 7,
transmits a D2D signal to another UE at a second subframe, and
receives a D2D signal from another UE at a third subframe. Through
the above-mentioned operation, the interference problem encountered
between D2D communication and eNB communication can be solved, and
D2D communication has Tx/Rx structures on a subframe basis and can
be easily multiplexed with the eNB communication in a time
domain.
[0062] In this case, if D2D communication has the Tx/Rx structure
on a subframe basis, this means that a time domain occupied by one
D2D Tx signal is a time domain occupied by one subframe, and a
basic time unit in which the UE transmits or receives the D2D
signal is used as one subframe. Needless to say, concatenation of
plural subframes may be achieved in units of a basic time as
necessary.
[0063] Meanwhile, the situation in which D2D communication has a
subframe-based structure may be efficiently used even when a UE
located outside of the eNB coverage performs D2D communication. For
example, even when a specific UE is located outside of the eNB
coverage, the subframe-based structure has an advantage in that a
UE acting as a target object of D2D communication can communicate
with the eNB using some subframes contained in the eNB coverage. In
addition, even when all D2D UEs are located outside of the eNB
coverage, the subframe-based structure has an advantage, because
communication is achieved in a manner that different D2D links
occupy different subframes when several D2D communication links are
contiguous to each other as shown in FIG. 6, resulting in avoidance
of mutual interference.
[0064] In order to perform D2D communication on a subframe basis, a
boundary position at which the subframe begins must be definitely
recognized by UEs participating in D2D communication. As a general
method for recognizing the subframe boundary, a reference signal
(hereinafter referred to as a subframe reference signal) having
unique attributes indicating the subframe boundary is transmitted,
and the UEs having received the reference signal can derive the
subframe boundary from the corresponding subframe reference signal
(RS) position. For example, a specific position spaced apart from a
reception (Rx) time of the subframe RS by a predetermined distance
may be determined to be the subframe boundary.
[0065] If D2D UE is located in the eNB coverage, the eNB can
transmit this subframe RS. Specifically, the subframe RS
transmitted from the eNB is not separately transmitted for D2D, and
the subframe RS may be transmitted to configure the subframe
position of the legacy eNB-UE communication. That is, a UE located
in the eNB coverage may receive a specific signal from the eNB so
as to initially access the eNB. In the case of the LTE system, it
is assumed that the UE located in the eNB coverage may receive a
primary synchronization signal (PSS) and/or a secondary
synchronization signal (SSS) and may recognize a boundary of a
subframe managed by the eNB using the PSS or SSS, so that this
subframe boundary may be applied to D2D communication without
change or may be modified according to a predetermined rule and
then applied to D2D communication.
[0066] In contrast, if D2D UE is located outside of the eNB
coverage, it is impossible to perform the above-mentioned
operation. Thus, the UE must directly transmit the subframe RS in
such a manner that the subframe boundaries between D2D UEs are
identical to each other.
First Embodiment
[0067] A method for allowing the UE to transmit the subframe RS
will hereinafter be described in detail.
[0068] If the UE transmits the subframe RS, it is preferable that
one subframe RS be transmitted among contiguous UEs. For this
purpose, when a specific UE attempts to transmit the subframe RS,
the presence or absence of a subframe RS transmitted from another
UE is confirmed at the initially designated time point. The first
embodiment proposes a method for transmitting the subframe RS at a
predetermined probability only when the subframe RS transmitted
from another UE is not present. That is, several UEs observe the
position of subframe RS candidates. If each UE does not detect any
subframe RS at a previous candidate position, the UE attempts to
transmit the subframe RS with a predetermined probability at the
next candidate position.
[0069] FIG. 8 illustrates a method for transmitting a subframe
reference signal (RS) according to a first embodiment of the
present invention.
[0070] Referring to FIG. 8, it can be recognized that no subframe
RS is transmitted at candidate positions (1, 2, 3) for transmission
of the subframe RS, because RS transmission at all UEs is not
achieved in the step of deciding whether stochastic transmission is
performed. At the candidate position 4, UE1 determines transmission
at the stochastic transmission/non-transmission decision step, so
that UE1 can transmit the subframe RS. In addition, UEs having
received the subframe RS from another UE may regard the
corresponding RS as only one RS during at least a predetermined
time, and it is preferable that additional attempts to transmit the
subframe RS be stopped.
[0071] The above-mentioned operation in which only one UE from
among several UEs configured to stochastically transmit the
subframe RS can perform final transmission will hereinafter be
referred to as the subframe RS transmission scheme based on
UE-to-UE competition. Various methods for implementing the UE-to-UE
competition based subframe RS transmission scheme may include the
following first and second methods (1) and (2).
[0072] 1) In the process of deciding whether stochastic
transmission is achieved, random numbers are generated according to
a predetermined rule at each Tx candidate position. If each of the
random number is higher than (or less than) a reference value
decided by a given transmission probability, UEs can operate to
transmit the reference signal.
[0073] 2) Alternatively, random numbers are generated and stored
according to a predetermined rule (that is present between a
predetermined minimum value and a maximum value) at an initial
candidate position. If the subframe RS is not transmitted at each
candidate position, a predetermined value is subtracted from the
stored value and the subtraction result is stored again. If the
stored value is equal to or less than a predetermined reference by
repetition of such subtracting and storing actions, UEs may operate
in such a manner that the subframe RS can be transmitted.
[0074] If the subframe RS is transmitted according to the
above-mentioned rule, all D2D UEs having received the subframe RS
may determine the position of the subframe boundary on the basis of
the received subframe RS. D2D UE having transmitted the subframe RS
assumes that the subframe RS transmitted from the D2D UE has been
transferred to contiguous UEs, such that the position of subframe
boundary is decided. A detailed example of the subframe RS
transmission scheme based on UE-to-UE competition will be given
below.
[0075] FIG. 9 illustrates the positions of subframe reference
signal (RS) transmission candidates from the viewpoint of one UE
according to a first embodiment of the present invention.
Specifically, FIG. 9 illustrates that a time period corresponding
to one subframe is composed of a total of N candidate positions
ranging from 0 to N-1.
[0076] Referring to FIG. 9, one candidate position for subframe RS
transmission may include a transmission period of a signature of a
real reference signal (RS) and a guard period configured to
guarantee a specific time needed for switching to the Rx position
at the next candidate position after completion of transmission. In
this case, the guard period may be omitted if the switching time to
the Rx operation is unnecessary.
[0077] Especially, the frequency position of a reference signal
(RS) transmitted at each candidate position by a UE and/or the
signature may be determined by an index of the candidate position.
For example, the signature of the RS transmitted at the candidate
position (n) may be prescribed to be transmitted in a frequency
domain corresponding to the corresponding candidate position, and
the signature having been transmitted at another candidate position
and the signature of the RS having been transmitted at the
candidate position (n) may occupy different frequency domains. In
addition, the signature of the RS having been transmitted at the
candidate position (n) may be prescribed to use a sequence
different from those of other candidate positions. For example, the
index (n) of the candidate position may be contained in a specific
value for initializing the sequence of the signature. Of course,
information regarding a predetermined number of bits is added to
the subframe RS so that the candidate position can be
indicated.
[0078] Through the above-mentioned operation, a UE having received
the signature of a specific subframe RS may allow another UE having
transmitted the corresponding signature to recognize which
candidate position is associated with the corresponding signature
from the viewpoint of a UE having transmitted the corresponding
signature, as well as to recognize which candidate position is a
transmission position of the corresponding signature. Therefore,
the reception (Rx) UE may recognize the subframe boundary from the
viewpoint of the corresponding Tx UE on the basis of the Rx time of
the corresponding signature and the candidate position index of the
corresponding signature.
[0079] Meanwhile, some last candidate positions may be used to
transmit a validation signal indicating whether the subframe RS is
successfully transmitted. That is, assuming that a specific D2D UE
has successfully received the subframe RS at the internal candidate
position of a specific subframe, the validation signal is
transmitted at the last candidate position so as to inform the
transmission UE of successful reception. Transmission of such
validation signal may have a relay effect of the subframe RS. In
addition, the validation signal may not always be transmitted at
the same subframe as the subframe RS, or may not always be
transmitted at the last candidate position. The validation signal
may be transmitted at a predetermined candidate position or may
also be transmitted after successful transmission of the subframe
RS.
[0080] FIG. 10 illustrates reception of a subframe reference signal
(RS) and transmission of a validation signal according to a first
embodiment of the present invention.
[0081] Referring to FIG. 10, under the condition that one subframe
is composed of a total of 6 candidate positions, a UE may receive
the subframe RS at the candidate position 2. After lapse of three
candidate positions, the UE may recognize the appearance of a new
subframe boundary. Thereafter, the UE may transmit the validation
signal at the candidate position 5 indicating the last candidate
position of the corresponding subframe.
[0082] The validation signal may be identical in structure to the
subframe RS. For distinction of the validation signal, the
validation signal may occupy the frequency position and/or may be
discriminated on the signature in association with other subframe
RSs. A UE (i.e., a head UE) having transmitted the subframe RS at a
specific subframe may determine that the subframe RS has been
successfully transmitted on the condition that the validation
signal of the corresponding subframe is detected, and thus D2D
communication is carried out in response to the subframe
boundary.
[0083] Specifically, all or some UEs having received the subframe
RS may simultaneously transmit the validation signal. In this case,
the validation signal may be configured in the form of overlap of
several UE transmission signals, so that the validation signal may
be transmitted at higher power. If a specific UE does not receive
the subframe RS at a specific subframe and receives the validation
signal for the subframe RS at the specific subframe, the subframe
boundary may be established on the basis of the validation signal.
However, there is a possibility that a specific UE from among UEs
having received the subframe RS receives different subframe RSs
having higher power. This specific UE may not participate in
simultaneous transmission of the validation signal. The
above-mentioned situation may indicate that a UE can select one of
several subframe RSs having been received by the UE and transmit
the validation signal corresponding to the selected subframe RS.
The UE having transmitted the subframe RS may assume that the
reference signal (RS) having been transmitted from the UE has been
received with available maximum power.
[0084] A specific UE may receive a plurality of subframe RSs
overlapping with each other at intervals of a long time difference
within a specific subframe, and a detailed description thereof will
hereinafter be given with reference to the attached drawings. FIG.
11 is a conceptual diagram illustrating an exemplary case of
receiving a plurality of overlapped subframe reference signals
(RSs) according to a first embodiment of the present invention.
[0085] In this case, the UE may recognize the occurrence of a
reception failure of the subframe RS (i.e., collision of the
subframe RS), so that the UE may not transmit the validation
signal. Alternatively, a non-validation signal indicating the
occurrence of collision between the subframe RSs may also be
transmitted.
[0086] The subframe RS transmission UEs, that have not received the
validation signal or have received the non-validation signal, may
assume failure of subframe boundary acquisition within the
corresponding subframe, and may re-perform competition-based
subframe RS transmission within the next subframe. Under the
condition that a specific UE transmits the subframe RS, does not
receive the validation signal corresponding to its own Tx signal,
and receives the validation signal corresponding to another
subframe RS, the subframe boundary may be formed in response to the
received validation signal.
[0087] Meanwhile, according to another method for transmitting the
validation signal when the competition-based subframe RS
transmission scheme is used, if a specific UE has received the
subframe RS valid at the candidate position (n), the subframe RSs
having the same attributes as those of the corresponding subframe
RS may be transmitted at all subsequent candidate positions (i.e.,
candidate positions n+1, n+2, etc.). Assuming that one specific UE
from among a plurality of competitive UEs of one group initially
transmits the subframe RS, all the remaining UEs having received
the subframe RS may simultaneously transmit the same subframe RS at
the subsequent candidate positions, such that the subframe RS can
be propagated to a wider region.
Second Embodiment
[0088] Meanwhile, the above-mentioned subframe RS transmission
scheme based on UE-to-UE competition may be efficiently used when
all UEs are located outside of the eNB coverage. Therefore, the
competition-based subframe RS transmission scheme can be applied
only to the case in which the UE is located outside of the eNB
coverage. In the case of the UE located in the eNB coverage, the
competition-based subframe RS transmission scheme may be applied
only to the case in which the use of UE-to-UE competition based
subframe RS transmission scheme is explicitly indicated.
[0089] The fact that the UE is located outside of the eNB coverage
may indicate a first case (a) in which PSS/SSS transmitted from the
eNB is not detected at a specific carrier, or a second case (b) in
which maximum RSRP and/or RSRQ measured at the specific carrier may
be equal to or less than a specific reference value.
[0090] In this case, the specific carrier is a carrier needed for
D2D communication. Specifically, if D2D communication is performed
in a downlink carrier of the FDD system, or if D2D communication is
performed in a carrier connected to the carrier needed for the D2D
communication (i.e., if D2D communication is performed in an uplink
carrier of the FDD system), the specific carrier may be a downlink
carrier paired with the uplink carrier at which the corresponding
D2D communication is scheduled to be executed. Alternatively, if it
is impossible to access the eNB through any carrier, a reference
may also be changed to the case in which the UE satisfies the
above-mentioned condition in all carriers capable of being
received, so that the UE-to-UE competition based subframe RS
transmission scheme can be restricted.
[0091] If some UEs are located in the eNB coverage, and if a UE
configured to perform D2D communication with the corresponding UE
establishes the subframe boundary on the basis of an arbitrary time
at the outside of the eNB coverage, it becomes difficult to perform
the above-mentioned operations. Preferably, the subframe boundary
for D2D communication of the corresponding UE may be identical to
that for eNB communication. The present invention may allow a UE
located in the eNB coverage to have priority over the other UE
located outside of the eNB coverage in terms of subframe RS
transmission. For such priority assignment, the following methods
(a) and (b) may be used.
[0092] a) First of all, there may be a low possibility that the UE
located outside of the eNB coverage transmits the subframe RS, and
there may be a high possibility that the UE located in the eNB
coverage transmits the subframe RS. Method (a) may be implemented
according to Method (1) from among the competition-based subframe
RS transmission methods. In more detail, a reference value used by
a UE located outside of the eNB coverage may be adjusted to be less
than a reference value used by the other UE located in the eNB
coverage (when the subframe RS is transmitted using random numbers
each of which is less than a reference value), or may be adjusted
to be higher than the reference value used by the other UE located
in the eNB coverage (when the subframe RS is transmitted using
random numbers each of which is higher than a reference value),
such that the method (a) can be implemented. If the method (a) is
applied to the method (2) from among the competition-based subframe
RS transmission methods, a maximum random number generated from the
UE located outside of the eNB coverage is adjusted to be higher
than a maximum random number generated from the other UE located in
the eNB coverage, so that the method (a) can be implemented.
[0093] b) Alternatively, the UE located outside of the eNB coverage
does not transmit the subframe RS at some initial Tx candidate
positions, such that the corresponding candidate position may be
used for the Tx operation of the UE located in the eNB coverage. If
the method (b) is applied to the method (a) from among the
competition-based subframe RS transmission methods, the method (b)
may be implemented by setting the value of 0 to the Tx probability
of the UE located outside of the eNB coverage at some initial
candidate positions. If the method (b) is applied to the method (a)
from among the competition-based subframe RS transmission methods,
a minimum random number generated from the UE located outside of
the eNB coverage may be adjusted to be higher than a minimum random
number generated from the other UE located in the eNB coverage, so
that the method (b) can be implemented. In addition, a minimum
random number generated from the UE located outside of the eNB
coverage may be adjusted to be equal to or higher than a minimum
random number generated from the other UE located in the eNB
coverage, so that the UE located outside of the eNB coverage may
always perform transmission after completion of the operations of
the UE located in the eNB coverage.
[0094] In addition, assuming that a valid period is present when a
selected subframe RS is used, UEs may re-transmit the subframe RS
on the basis of competition, after the corresponding valid period
has expired. In this case, an expiration time of the valid period
may be immediately set to the start time of the subframe RS
transmission time candidate positions. In the case of using the
method (1) from among the competition-based subframe RS
transmission methods, if the UE generates a random number value and
does not transmit the RS at the candidate position, the UE may
begin to reduce the random number value as soon as the valid period
of a previous RS has expired. In the case of using the method (2)
from among the competition-based subframe RS transmission methods,
the UE having low priority and located outside of the eNB coverage
may not transmit the subframe RS during a predetermined time
starting from the expiration time of the valid time of a subframe
RS used as a legacy reference.
Third Embodiment
[0095] Meanwhile, the UE located in the eNB coverage can acquire
the subframe boundary on the basis of the signal transmitted from
the eNB as described above, but there is a need for the UE located
in the eNB coverage to transmit the subframe RS in such a manner
that the other UE located outside of the eNB coverage can obtain
the same subframe boundary. For this purpose, the eNB may command a
specific UE to transmit the subframe RS through higher layer
signaling such as RRC signaling.
[0096] This transmission indication may be classified into direct
indication and indirect indication. The direct indication may
explicitly indicate the position of time/frequency resources of the
subframe RS, the signature information of RS, Tx power, etc., that
are scheduled to be transmitted from the corresponding UE to a
specific UE. The indirect indication may allow the eNB to transmit
the subframe RS to either a specific UE or a UE group composed of
some UEs according to the competition-based subframe RS
transmission method. This indirect indication may include
attributes of the subframe RS, for example, the position of
time/frequency resources of the RS, the signature information of
the RS, Tx power, etc.
[0097] After the UE located in the eNB coverage receives the
transmission (Tx) indication of the eNB, the UE may transmit the
subframe RS according to the received Tx indication. Downlink
resources are excessively interfered with by high Tx power of the
eNB, so that an arrival region of the subframe RS may be
excessively limited, and UL resources may be used as the subframe
RS transmission resources.
[0098] A start point of the UL subframe is adjusted according to
different timing advance values of individual UEs so as to offset
the propagation delay between the eNB and the UE, and thus Tx
signals of several UEs can arrive at the eNB at the same time
point. As a result, a boundary of a downlink subframe of the UE
located in the eNB coverage is different from a boundary of an
uplink subframe of the UE located in the eNB coverage. FIG. 12 is a
conceptual diagram illustrating that a boundary of a downlink
subframe and a boundary of an uplink subframe are changed according
to a third embodiment of the present invention.
[0099] In this case, the UE having received a transmission
indication message of the subframe RS from the eNB has to determine
which one of the DL subframe boundary and the UL subframe boundary
will be used for transmission of the subframe RS. One of the
following subframe RS transmission time decision methods may be
used as necessary.
[0100] i) As a first subframe RS transmission (Tx) time decision
method, the subframe RS transmission time may be determined on the
basis of the DL subframe boundary.
[0101] A reference signal (RS) transmitted from the UE may be
transmitted at the boundary position of the DL subframe received by
the UE, or may be transmitted at a specific position shifted from
the DL subframe boundary position by a predetermined time.
[0102] FIG. 13 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) using a boundary of a downlink subframe according to a third
embodiment of the present invention. Specifically, FIG. 13
illustrates that the subframe RS is delayed from the DL subframe
boundary position by a predetermined time (i.e., offset), and is
then transmitted. In FIG. 13, it is assumed that UE1 located in the
coverage transmits the subframe RS to a UE2 located outside of the
coverage. Of course, the subframe RS may also be transmitted at a
specific time earlier than a predetermined time (i.e., offset) on
the basis of the DL subframe boundary without departing from the
scope or spirit of the present invention.
[0103] The above-mentioned scheme has an advantage in that the
boundary position of the DL subframe of the UE (having transmitted
the corresponding subframe RS) located in the coverage can be
recognized by other UEs located outside of the coverage.
Specifically, in the case of using a TDD system, when the signal
transmitted from an external UE of the coverage for D2D
communication may cause strong interference to the internal UE of
the coverage when the internal UE of the coverage receives the DL
signal. In this case, assuming that the external UE of the coverage
can recognize the DL subframe boundary position of the internal UE
of the coverage, downlink signal reception of the internal UE of
the corresponding coverage can be more efficiently protected, and a
detailed description thereof will hereinafter be given with
reference to the attached drawings.
[0104] FIG. 14 is a conceptual diagram illustrating another method
for determining a transmission (Tx) time of a subframe reference
signal (RS) using a boundary of a downlink subframe according to a
third embodiment of the present invention.
[0105] Referring to FIG. 14, transmission of a D2D signal is
excluded in a predetermined time section derived from the subframe
boundary position received by the external UE of the coverage, so
that reception of the important DL signals of the internal UE of a
contiguous coverage can be protected. Alternatively, during the
corresponding time section, D2D transmission power may be reduced
by a predetermined offset, or maximum Tx power may be set to lower
power, DL signal reception of the internal UE of the coverage can
be protected but the D2D communication with a contiguous UE located
very close to the internal UE may be allowed.
[0106] In FIG. 14, UE1 may readjust the subframe #3 in response to
the DL subframe boundary, and may use the subframe #3 for
transmission of the subframe RS. UE2 located outside of the
coverage may acquire an estimation value of the DL subframe
boundary of UE1, and may not apply a time section decided by a
predetermined rule on the basis of the corresponding estimation
value to D2D communication, such that UE1 may easily receive the DL
signal at the subframe #1 and the subframe #2. In this case, the
section unused for D2D communication may repeatedly appear.
[0107] In addition, if the subframe RS is transmitted in response
to the DL subframe boundary as described above, a subsequent D2D
Tx/Rx signal may also be transmitted and received on the basis of
the DL subframe boundary. Specifically, the subsequent D2D Tx/Rx
signal may also be applied to the D2D signal through which data can
be transmitted using a large amount of resources. Meanwhile, a D2D
discovery signal for recognizing whether a UE is located at a
contiguous position may also have different subframe
boundaries.
[0108] ii) As a second subframe RS transmission (Tx) time decision
method, the subframe RS transmission time may be determined on the
basis of the UL subframe boundary.
[0109] The RS transmitted by a UE may be transmitted at the UL
subframe boundary at which the UE transmits the RS to the eNB, or
may be transmitted at a specific position shifted from the UL
subframe boundary by a predetermined time.
[0110] FIG. 15 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) using a boundary of an uplink subframe according to a third
embodiment of the present invention. In FIG. 15, it is assumed that
UE1 located in the coverage transmits the subframe RS to UE2
located outside of the coverage.
[0111] The above-mentioned scheme is characterized in that the
external UE of the coverage can acquire the UL subframe boundary of
the internal UE of the coverage, such that the internal UE of the
coverage can perform D2D communication with the external UE of the
coverage, and at the same time can easily perform signal
transmission to the eNB at another contiguous UL subframe.
Specifically, the above-mentioned advantage may be considered
effective in the FDD system in which all subframes of a specific
frequency domain are set to the UL subframes. In this case, the DL
subframes are separated from the UL subframes having D2D
communication in the frequency domain, so that a guard period for
DL reception shown in FIG. 14 need not be used.
[0112] In addition, if the subframe RS is transmitted in response
to the UL subframe boundary, a subsequent D2D Tx/Rx signal may also
be transmitted and received on the basis of the UL subframe
boundary. Specifically, the subsequent D2D Tx/Rx signal may also be
applied to the D2D signal through which data can be transmitted
using a large amount of resources. Likewise, a D2D discovery signal
for recognizing whether a UE is located at a contiguous position
may also have different subframe boundaries.
[0113] iii) As a third subframe RS transmission (Tx) time decision
method, the subframe RS transmission time may also be determined
between the UL subframe boundary and the DL subframe boundary.
[0114] For example, the subframe RS transmission time may be set to
a specific time earlier than the DL subframe boundary by a
predetermined time corresponding to a half of a current TA value,
or may also be set to a specific time spaced apart from the
corresponding time by a predetermined time.
[0115] FIG. 16 is a conceptual diagram illustrating a method for
determining a transmission (Tx) time of a subframe reference signal
(RS) at a time between a boundary of an uplink subframe and a
boundary of a downlink subframe according to a third embodiment of
the present invention. Specifically, as can be seen from FIG. 16, a
half of TA is approximately identical to a propagation delay
between the eNB and the UE, so that a time earlier than the DL
subframe boundary reception time by a predetermined time
corresponding to the half of TA is identical to the transmission
time at which the eNB transmits the DL subframe boundary, and is
also identical to the reception time at which the eNB receives the
UL subframe boundary.
[0116] Therefore, a specific time earlier than the DL subframe
boundary reception time by a predetermined time corresponding to
half the TA is approximately identical in all UEs belonging to the
same cell. As a result, although any UE transmits the subframe RS,
the subframe RS is transmitted at the approximately similar time
points, so that the overall D2D subframe boundary remains unchanged
even when several UEs alternately transmit the subframe RS.
[0117] In order to select one method from among the above-mentioned
subframe RS transmission time decision methods, the eNB may inform
the UE of a specific signal indicating which decision method will
be used for transmission of the subframe RS. Alternatively, the
respective methods have advantages in terms of different duplex
methods, such that the corresponding method can be selected
according to which duplex scheme is used by resources to be used
for transmission of the subframe RS. For example, the TDD system
may use the subframe RS transmission time decision method (i) based
on the DL subframe boundary, and the FDD system may use the other
subframe RS transmission time decision method (ii) based on the
ULsubframe boundary.
[0118] Alternatively, the subframe RSs having different attributes
may also be transmitted in response to a plurality of subframe RSs.
For example, in the case of using a discovery signal that is
simultaneously transmitted/received by several UEs in response to
synchronization, all UEs participating in transmission must have a
common time, a UE may transmit the RS according to either the
method (iii) for determining the subframe RS transmission time
between the boundary of the UL subframe and the boundary of the DL
subframe or the other method (i) for determining the subframe RS
transmission time when there is a little difference in propagation
delay between UEs, and may transmit and receive the discovery
signal on the basis of the RS transmission result. In contrast,
when exchanging user data between individual UEs, the method (ii)
for determining the subframe RS transmission time may be used
according to a situation of each UE.
[0119] In this case, it is necessary for UEs to recognize which one
of the time decision methods is used for transmission of the
subframe RS, such that the subframe RSs transmitted according to
different schemes (i.e., the subframe RSs for synchronization of
different types of D2D signals) may be differentiated at the Tx
signature, the positions of the transmitted time/frequency domains,
or the like. For example, the signature of a specific subframe RS
may be predefined in such a manner that the signature can be used
only for the subframe RS for the discovery signal or can be used
only for the subframe RS for D2D communication.
Fourth Embodiment
[0120] Meanwhile, if the UE located in the coverage (i.e., the
internal UE of the coverage) receives an indication message of the
subframe RS transmission from the eNB, the UE operation
(specifically, collision with UL transmission toward the eNB) may
occur in the corresponding resources.
[0121] In this case, transmission of the subframe RS may have
priority. That is, when a UE configured to transmit the subframe RS
at a specific subframe attempts to transmit a signal to the eNB at
the same subframe, the signal to be transmitted to the eNB may be
dropped and the subframe RS may then be transmitted.
[0122] Alternatively, signal transmission to the eNB may also have
priority. That is, when a UE configured to transmit the subframe RS
in a specific subframe attempts to transmit a signal to the eNB in
the same subframe as the specific subframe, RS transmission may be
dropped and signal transmission to the eNB may then be carried
out.
[0123] The above-mentioned methods may be used in different ways
according to a method for indicating transmission of the subframe
RS or according to categories of signals to be transmitted to the
eNB. For example, assuming that the signal to be transmitted to the
eNB is any one of a semi-statically transmitted semi-persistent
scheduling (SPS) signal, a periodic CSI report, and a scheduling
request signal to be independently transmitted by the UE, the eNB
may not directly decide transmission of the corresponding time, so
that the subframe RS may have priority. Specifically, the
above-mentioned case may be more effectively used for the case in
which the eNB directly indicates the subframe RS.
[0124] In another example, assuming that the signal to be
transmitted to the eNB is a PDSCH indicated by a physical layer
signal such as PDCCH or EPDCCH (Enhanced PDCCH), HARQ-ACK regarding
an SPS-based PDSCH, an uplink grant, or a PHICH-based PUSCH
transmission signal, signal transmission to the eNB may have
priority. Upon receiving an indication message that commands the UE
to competitively transmit the subframe RS, i.e., upon receiving an
indirect indication message indicating transmission of the subframe
RS, the subframe RS may also be transmitted at another time, such
that signal transmission to the eNB may always have priority as
necessary.
[0125] As described above, the subframe RS having been transmitted
by the direct indication message or the indirect indication message
of the eNB may be classified into the subframe RS being
autonomously determined by the UE without receiving the indication
message from the eNB, and the signature attributes. For example, a
subset is selected from among all sets of the signature capable of
being used as a signature of the subframe RS, and the signature
corresponding to the corresponding subset may be defined to be
transmitted by the UE only when direct/indirect indication messages
of the eNB are present. Of course, an additional indicator may be
used, and it may be possible to define an additional indicator for
discriminating between the subframe RS having been transmitted
without using the indication message of the eNB and the subframe
having been transmitted by the indication message of the eNB. As a
result, if a specific UE receives a specific subframe RS, it can be
recognized whether the RS has been transmitted by the indication
message of the eNB, i.e., it can be recognized whether the RS has
been transmitted by the UE located in the eNB coverage. Based on
the above-mentioned information, higher priority may be
successively assigned to transmission of the RS of the UE located
in the eNB coverage.
[0126] In addition, when the validation signal disclosed in the
first embodiment is constructed, all or some of attributes of the
subframe RS having been received by the UE may be reused. As a
result, if the subframe RS is transmitted by the indication message
of the eNB, the fact that the validation signal has been
transmitted by the indication message of the eNB may be signaled to
other UEs. Accordingly, a D2D UE, that has received the subframe RS
transmitted by the validation signal or the eNB indication message,
may retransmit the corresponding subframe RS without using
additional UE-to-UE competition at a specific time, or may
retransmit the corresponding subframe RS simultaneously while
having priority in competition. Boundary information of the
subframe used in the eNB may be propagated to the external UEs of
the coverage.
[0127] FIG. 17 is a conceptual diagram illustrating a method for
propagating boundary information of a subframe used in eNB to UEs
located outside of a coverage region according to a fourth
embodiment of the present invention.
[0128] Referring to FIG. 17, the eNB may command a UE1 to transmit
the subframe RS, and the UE1 may transmit the subframe RS according
to the eNB indication message. UE2 may transmit the subframe RS
having the highest priority from among the subframe RS received
from UE1 and other subframe RSs, or may transmit the validation
signal in response to transmission of the highest-priority subframe
RS.
[0129] Through the above-mentioned propagation process, although
UE3 does not directly perform D2D communication with the internal
UE of the eNB coverage, the UE3 can be synchronized with the
subframe of the eNB, such that the UE1 located in the coverage and
the UE2 configured to perform D2D communication may be helpful to
the D2D operation of the UE2.
[0130] In addition, when a first external UE of the coverage
performs D2D communication in response to the subframe RS
transmitted either by the first external UE or by a second external
UE of the coverage, detection of the subframe RS transmitted by the
internal UE of the coverage is attempted. If the subframe RS is
detected, the first external UE may operate in response to the
subframe RS transmitted by the internal UE of the coverage. For
example, the coverage external UE having detected the subframe RS
transmitted by the internal UE of the coverage may reconfigure the
subframe time point in response to the RS transmitted by the
coverage internal UE within a predetermined time. If the
corresponding UE transmits the subframe RS, the RS may be
transmitted in response to the reconfigured subframe time, or RS
transmission of the corresponding UE may be stopped.
[0131] In addition, assuming that a valid period is present in the
subframe RS that has been transmitted by the coverage external UE
and used as a reference of the legacy D2D communication,
synchronization with the subframe RS transmitted by the coverage
external UE is maintained until the corresponding valid period
expires. However, after the valid time has expired, synchronization
with a start time of the subframe RS transmitted by the internal UE
of the coverage is needed. Alternatively, it is expected that
another subframe RS will be transmitted by the internal UE of the
coverage within a predetermined time, and transmission of the
subframe RS is not attempted during the corresponding predetermined
time, such that priority may be assigned to the internal UE of the
coverage. In this case, the coverage external UE that has not
received the subframe RS during the predetermined time may attempt
to transmit the subframe RS according to the above stochastic
methods.
[0132] Meanwhile, according to the subframe RS transmission scheme
based on UE-to-UE competition, priority for RS transmission may be
differently assigned according to D2D UE categories. For example,
UEs for D2D communication may be classified into some categories
according to various kinds of information, for example, maximum Tx
power of the D2D signal, information as to whether group
communication is possible (i.e., whether one D2D UE can
simultaneously perform D2D communication with a plurality of D2D
UEs), and information as to whether other D2D links can be
controlled. Specifically, control of another D2D link may indicate
control of resource allocation regarding a contiguous D2D link in
which the corresponding UE is not contained. In this case, priority
may be differently assigned to transmission of the subframe RS
according to D2D UE categories. Higher priority may be assigned to
UE categories having higher function. For example, higher priority
may be assigned to a UE having a higher maximum Tx power, a UE
having group communication capability, or a UE having a control
function of another D2D link, such that the corresponding UEs may
establish the subframe reference at higher probability and other
UEs may operate in response to the established reference.
[0133] In addition, although a UE acquires the subframe boundary
according to the above-mentioned scheme, a new subframe boundary
must be determined in response to the movement of D2D UEs, such
that it is impossible for synchronization having been acquired once
to be indefinitely valid. Therefore, a valid period is established
in the subframe boundary having been decided once. After this valid
period has expired, the subframe boundary may be re-established
after completion of the subframe RS transmission process. In this
case, assuming that UE-to-UE competition is performed for each
subframe boundary reconfiguration time, an unnecessary time delay
may occur due to UE-to-UE RS collision.
[0134] In order to address the above problem, priority may be
assigned to a UE having transmitted the valid subframe RS when
deciding the legacy subframe boundary. The method for assigning
such priority may be identical to the method for assigning priority
to the internal UE of the eNB coverage for use in the
above-mentioned RS transmission priority assignment method. In
addition, the UE having transmitted the valid subframe RS when
deciding the legacy subframe boundary may be assigned priority by
transmitting the validation signal irrespective of transmission of
other subframe RSs.
[0135] A UE in which a new D2D link is activated may maintain the
same subframe boundary as in legacy peripheral UEs performing
legacy D2D communication. For this purpose, the UE in which a new
D2D link is activated does not transmit the subframe RS during a
predetermined time, and may determine the presence or absence of
the subframe RSs transmitted from the legacy D2D UEs.
[0136] In this case, the predetermined time in which no subframe RS
is transmitted is set to a valid period of the subframe boundary
determined once. If a UE performing the legacy D2D communication is
located at an adjacent position, the subframe RS may be transmitted
at least once within the predetermined time. If the UE in which the
new D2D link is activated does not detect the valid subframe RS or
the validation signal during the predetermined time, the UE may
directly attempt to transmit the subframe RS.
Fifth Embodiment
[0137] Information regarding various parameters to be used in
actual D2D communication may be contained in the subframe RS. As a
result, UEs having received the same subframe RS may perform D2D
communication using the same parameters.
[0138] Parameters capable of being contained in the subframe RS are
as follows.
[0139] (1) The position and size information of a frequency domain
in which D2D communication will be executed. [0140] D2D
communication may be achieved in a region corresponding to the
above size information on the basis of a frequency domain having
received the subframe RS.
[0141] (2) Transmission (Tx) power information to be used for D2D
communication, for example, maximum Tx power or various parameters
shown in a Tx power control equation. [0142] If the legacy PUSCH Tx
power control scheme shown in the following equation 1 is used
between the eNB and the UE without change, parameters
(P.sub.O.sub.--.sub.PUSCH,c(j), .alpha..sub.c(j)) are represented
by the following equation 1.
[0142] P PUSCH , c ( i ) = min { P CMAX , c ( i ) 10 log 10 ( M
PUSCH , c ( i ) ) + P O_PUSCH , c ( j ) + .alpha. c ( j ) PL c +
.DELTA. TF , c ( i ) + f c ( i ) [ Equation 1 ] ##EQU00001##
[0143] In Equation 1, a unit of P.sub.O.sub.--.sub.PUSCH,c(j) is
dBm, and P.sub.O.sub.--.sub.PUSCH,c(j) denotes PUSCH Tx power of a
carrier (c) at the i-th time. Specifically, P.sub.CMAX,c(i) is
maximum Tx power of a UE of the carrier (c), c is a pathloss
estimation value of a downlink signal, .alpha..sub.c(j) and 10
log.sub.10(M.sub.PUSCH,c(i))+P.sub.O.sub.--.sub.PUSCH,c(j) denote
parameters on the basis of a higher layer signal of the carrier (c)
at the i-th time, attributes of data to be transmitted at the i-th
time, the amount of allocated resources, etc. The parameters may
correspond to the open-loop power control. Finally, f.sub.e(i) is a
power control value of the i-th time decided by information
contained in a closed-loop power control message received from the
eNB, and may correspond to a parameter for closed-loop power
control.
[0144] (3) Length information of Cyclic Prefix (CP) to be used for
D2D communication [0145] This length information (3) may indicate
whether a normal CP or an extended CP will be used, or may indicate
whether a new-length CP will be used on the condition that the
new-length CP is additionally introduced for D2D communication.
[0146] (4) Length of a time unit of a single D2D transmission
[0147] This length information (4) may indicate whether a single
D2D Tx signal is transmitted using one subframe as a time
reference, may indicate whether a single D2D Tx signal is
transmitted using several concatenated subframes as a single time
reference, or may indicate the number of concatenated subframes
when several subframes are concatenated.
[0148] (5) Contention parameters for D2D signal transmission [0149]
If UEs transmit a D2D signal on the basis of contention, the
contention parameters are parameters to be used for contention. For
example, the contention parameters may include a transmission (Tx)
probability value to be used when each UE stochastically transmits
the D2D signal at each Tx time. In another example, each UE
generates/stores random numbers within a predetermined region, and
subtracts a predetermined value from the random numbers whenever a
channel is empty. If the subtraction result is equal to or less
than a predetermined reference, the contention parameters may
include information regarding a generation region of random numbers
to be used when transmission is performed.
[0150] As a representative example of the method for including such
information in the subframe RS, when the signature of the subframe
RS is generated, the parameter values may be used as variables.
Alternatively, an additional channel for transmitting the above
information using constant time/frequency domains derived from the
corresponding signature may be formed separately from the signature
of the subframe RS. For example, the above-mentioned information
may be transmitted only during a predetermined time after
transmission of the signature, and the above-mentioned information
may be transmitted through a channel transmitted using the same
frequency domain as in the signature.
[0151] The above-mentioned information may be set to a specific
value contained in the eNB indication when the corresponding UE
transmits a channel having the subframe RS or the above information
upon receiving the eNB indication message. In contrast, if the
channel having the subframe RS or the above information is
transmitted without receiving the eNB indication message at the
outside of the eNB coverage or without receiving the subframe RS
initiated by the eNB indication at the outside of the eNB coverage,
the above-mentioned information may be set to a kind of default
value of each UE. That is, the UE may have a default value
corresponding to various kinds of information during transmission
of the subframe RS. If the subframe RS is transmitted according to
the eNB indication, this default value may be changed to a value
received from the eNB.
[0152] FIG. 18 is a block diagram for an example of a communication
device according to one embodiment of the present invention.
[0153] Referring to FIG. 18, a communication device 1800 may
include a processor 1810, a memory 1820, an RF module 1830, a
display module 1840, and a user interface module 1850.
[0154] Since the communication device 1800 is depicted for clarity
of description, prescribed module(s) may be omitted in part. The
communication device 1800 may further include necessary module(s).
And, a prescribed module of the communication device 1800 may be
divided into subdivided modules. A processor 1810 is configured to
perform an operation according to the embodiments of the present
invention illustrated with reference to drawings. In particular,
the detailed operation of the processor 1810 may refer to the
former contents described with reference to FIG. 1 to FIG. 17.
[0155] The memory 1820 is connected with the processor 1810 and
stores an operating system, applications, program codes, data, and
the like. The RF module 1830 is connected with the processor 1810
and then performs a function of converting a baseband signal to a
radio signal or a function of converting a radio signal to a
baseband signal. To this end, the RF module 1830 performs an analog
conversion, amplification, a filtering, and a frequency up
conversion, or performs processes inverse to the former processes.
The display module 1840 is connected with the processor 1810 and
displays various kinds of informations. And, the display module
1840 can be implemented using such a well-known component as an LCD
(liquid crystal display), an LED (light emitting diode), an OLED
(organic light emitting diode) display and the like, by which the
present invention may be non-limited. The user interface module
1850 is connected with the processor 1810 and can be configured in
a manner of being combined with such a well-known user interface as
a keypad, a touchscreen and the like.
[0156] The above-described embodiments correspond to combinations
of elements and features of the present invention in prescribed
forms. And, the respective elements or features may be considered
as selective unless they are explicitly mentioned. Each of the
elements or features can be implemented in a form failing to be
combined with other elements or features. Moreover, it is able to
implement an embodiment of the present invention by combining
elements and/or features together in part. A sequence of operations
explained for each embodiment of the present invention can be
modified. Some configurations or features of one embodiment can be
included in another embodiment or can be substituted for
corresponding configurations or features of another embodiment.
And, it is apparently understandable that an embodiment is
configured by combining claims failing to have relation of explicit
citation in the appended claims together or can be included as new
claims by amendment after filing an application.
[0157] Embodiments of the present invention can be implemented
using various means. For instance, embodiments of the present
invention can be implemented using hardware, firmware, software
and/or any combinations thereof. In the implementation by hardware,
a method according to each embodiment of the present invention can
be implemented by at least one selected from the group consisting
of ASICs (application specific integrated circuits), DSPs (digital
signal processors), DSPDs (digital signal processing devices), PLDs
(programmable logic devices), FPGAs (field programmable gate
arrays), processor, controller, microcontroller, microprocessor and
the like.
[0158] In case of the implementation by firmware or software, a
method according to each embodiment of the present invention can be
implemented by modules, procedures, and/or functions for performing
the above-explained functions or operations. Software code is
stored in a memory unit and is then drivable by a processor. The
memory unit is provided within or outside the processor to exchange
data with the processor through the various means known in
public.
[0159] While the present invention has been described and
illustrated herein with reference to the preferred embodiments
thereof, it will be apparent to those skilled in the art that
various modifications and variations can be made therein without
departing from the spirit and scope of the invention. Thus, it is
intended that the present invention covers the modifications and
variations of this invention that come within the scope of the
appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
[0160] As is apparent from the above description, although the
method and apparatus for acquiring synchronization for D2D direct
communication at the outside of a coverage region in a wireless
communication system have been disclosed on the basis of
application to 3GPP LTE, the inventive concept of the present
invention is applicable not only to 3GPP LTE, but also to other
wireless communication systems.
* * * * *