U.S. patent application number 16/524612 was filed with the patent office on 2019-11-14 for method for transmitting downlink in unlicensed band.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Joonkui AHN, Kijun KIM, Hanjun PARK.
Application Number | 20190349984 16/524612 |
Document ID | / |
Family ID | 56879207 |
Filed Date | 2019-11-14 |
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United States Patent
Application |
20190349984 |
Kind Code |
A1 |
AHN; Joonkui ; et
al. |
November 14, 2019 |
METHOD FOR TRANSMITTING DOWNLINK IN UNLICENSED BAND
Abstract
A method for performing uplink transmissions in an unlicensed
band is discussed. The method includes receiving, by a first user
equipment (UE) in a first group from a base station (BS), a first
uplink grant for a first uplink transmission in the unlicensed
band; receiving, by a second user equipment (UE) in a second group
from the BS, a second uplink grant for a second uplink transmission
in the unlicensed band; determining, by the first UE in the first
group, a first delay time to initiate first clear channel
assessment (CCA) in the unlicensed band from a reference time;
determining, by the second UE in the second group, a second delay
time to initiate second CCA in the unlicensed band from the
reference time; checking, by the first UE in the first group,
whether a channel is idle by performing the first CCA during a
first CCA duration after the first delay time from the reference
time; checking, by the second UE in the second group, whether the
channel is idle by performing the second CCA during a second CCA
duration after the second delay time from the reference time; and
performing, by the first and/or second UE, the first and/or second
uplink transmission based on the first and/or second uplink grant
when the channel is idle.
Inventors: |
AHN; Joonkui; (Seoul,
KR) ; KIM; Kijun; (Seoul, KR) ; PARK;
Hanjun; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
56879207 |
Appl. No.: |
16/524612 |
Filed: |
July 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15557325 |
Sep 11, 2017 |
10412759 |
|
|
PCT/KR2016/002477 |
Mar 11, 2016 |
|
|
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16524612 |
|
|
|
|
62132477 |
Mar 12, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 16/14 20130101;
H04W 72/14 20130101; H04W 74/0808 20130101 |
International
Class: |
H04W 72/14 20060101
H04W072/14; H04W 16/14 20060101 H04W016/14; H04W 74/08 20060101
H04W074/08 |
Claims
1. A method for performing uplink transmissions in an unlicensed
band, the method comprising: receiving, by a first user equipment
(UE) in a first group from a base station (BS), a first uplink
grant for a first uplink transmission in the unlicensed band;
receiving, by a second user equipment (UE) in a second group from
the BS, a second uplink grant for a second uplink transmission in
the unlicensed band; determining, by the first UE in the first
group, a first delay time to initiate first clear channel
assessment (CCA) in the unlicensed band from a reference time;
determining, by the second UE in the second group, a second delay
time to initiate second CCA in the unlicensed band from the
reference time; checking, by the first UE in the first group,
whether a channel is idle by performing the first CCA during a
first CCA duration after the first delay time from the reference
time; checking, by the second UE in the second group, whether the
channel is idle by performing the second CCA during a second CCA
duration after the second delay time from the reference time; and
performing, by the first and/or second UE, the first and/or second
uplink transmission based on the first and/or second uplink grant
when the channel is idle.
2. The method of claim 1, wherein the second delay time is longer
than the first delay time.
3. The method of claim 1, wherein the first uplink grant and second
uplink grant are allocated same as a single uplink grant.
4. The method of claim 1, wherein the first delay time is
determined based on a parameter specific to the first group, and
the second delay time is determined based on a parameter specific
to the second group.
5. The method of claim 1, wherein each of the first and second
uplink grants comprises information on a parameter used to
determine each of the first and second delay times.
6. The method of claim 1, wherein the reference time is a point
after a certain period of time from a time when the first or second
uplink grant is received.
7. The method of claim 1, wherein the first CCA duration is defined
in inverse proportion to the first delay time, and the second CCA
duration is defined in inverse proportion to the second delay
time.
8. The method of claim 1, wherein the first and/or second uplink
transmission is not performed when the channel is busy.
9. A device for performing uplink transmissions in an unlicensed
band, the device comprising: a transceiver to transmit and receive
a radio signal; and a processor coupled to the transceiver and
configured to: receive a first uplink grant for a first uplink
transmission in the unlicensed band; receive a second uplink grant
for a second uplink transmission in the unlicensed band; determine
a first delay time to initiate first clear channel assessment (CCA)
in the unlicensed band from a reference time; determine a second
delay time to initiate second CCA in the unlicensed band from the
reference time; check, whether a channel is idle by performing the
first CCA during a first CCA duration after the first delay time
from the reference time; check, whether the channel is idle by
performing the second CCA during a second CCA duration after the
second delay time from the reference time; and perform the first
and/or second uplink transmission based on the first and/or second
uplink grant when the channel is idle.
10. The device of claim 9, wherein the second delay time is longer
than the first delay time.
11. The device of claim 9, wherein the first uplink grant and
second uplink grant are allocated same as a single uplink
grant.
12. The device of claim 9, wherein the first delay time is
determined based on a parameter specific to the first group, and
the second delay time is determined based on a parameter specific
to the second group.
13. The device of claim 9, wherein each of the first and second
uplink grants comprises information on a parameter used to
determine each of the first and second delay times.
14. The device of claim 9, wherein the reference time is a point
after a certain period of time from a time when the first or second
uplink grant is received.
15. The device of claim 9, wherein the first CCA duration is
defined in inverse proportion to the first delay time, and the
second CCA duration is defined in inverse proportion to the second
delay time.
16. The device of claim 9, wherein the first and/or second uplink
transmission is not performed when the channel is busy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a Continuation of co-pending U.S. patent
application Ser. No. 15/557,325 filed on Sep. 11, 2017, which is
the National Phase of PCT International Application No.
PCT/KR2016/002477 filed on Mar. 11, 2016, which claims the priority
benefit under 35 U.S.C. .sctn. 119(e) to U.S. Provisional
Application No. 62/132,477 filed on Mar. 12, 2015, all of which are
hereby expressly incorporated by reference into the present
application.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to wireless communication, and
more particularly, to a method for downlink transmission in an
unlicensed band and a method for uplink transmission in an
unlicensed band.
Discussion of the Related Art
[0003] With the explosive increase in mobile data traffic in recent
years, a service provider has utilized a wireless local area
network (WLAN) to distribute the data traffic. Since the WLAN uses
an unlicensed band, the service provider can address a demand for a
significant amount of data without the cost of an additional
frequency. However, there is a problem in that an interference
phenomenon becomes serious due to a competitive WLAN installation
between the providers, quality of service (QoS) cannot be
guaranteed when there are many users, and mobility cannot be
supported. As one of methods for compensating this, a long term
evolution (LTE) service in the unlicensed band is emerged.
[0004] LTE in unlicensed spectrum (LTE-U) or licensed-assisted
access using LTE (LAA) is a technique in which an LTE licensed band
is used as an anchor to combine a licensed band and an unlicensed
band by the use of carrier aggregation (CA). A user equipment (UE)
first accesses a network in the licensed band. A base station (BS)
may offload traffic of the licensed band to the unlicensed band by
combining the licensed band and the unlicensed band according to a
situation.
[0005] The LTE-U may extend an advantage of LTE to the unlicensed
band to provide improved mobility, security, and communication
quality, and may increase a throughput since the LTE has higher
frequency efficiency than the legacy radio access technique.
[0006] Unlike the licensed band in which exclusive utilization is
guaranteed, the unlicensed band is shared with various radio access
techniques such as the WLAN. Therefore, each communication node
acquires a channel to be used in the unlicensed band in a
contention-based manner, and this is called a carrier sense
multiple access with collision avoidance (CSMA/CA). Each
communication node must perform channel sensing before transmitting
a signal to confirm whether a channel is idle, and this is called
clear channel assessment (CCA).
[0007] Since various wireless access techniques perform the CCA in
the unlicensed band, there is a need for a method capable of
reducing an interference.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method for downlink
transmission in an unlicensed band.
[0009] The present invention provides a method for uplink
transmission in an unlicensed band and a device using the same.
[0010] In an aspect, a method for downlink transmission in an
unlicensed band is provided. The method includes determining, by a
plurality of base stations (BSs) in a first group, a first delay
time to initiate clear channel assessment (CCA) in the unlicensed
band from a reference time, checking, by the plurality of BSs,
whether a channel is idle by performing CCA for CCA duration after
the first delay time from the reference time, and simultaneously
performing, by the plurality of BSs, downlink transmissions when
the channel is idle.
[0011] In another aspect, a method for uplink transmission in an
unlicensed band is provided. The method includes receiving, by a
wireless device, an uplink grant for uplink transmission in an
unlicensed band from a base station (BS), determining, by the
wireless device, a delay time to initiate clear channel assessment
(CCA) from a reference time, checking, by the wireless device,
whether a channel is idle by performing CCA for CCA duration after
the delay time from the reference time, and performing, by the
wireless device, uplink transmission based on the uplink grant when
the channel is idle.
[0012] In still another aspect, a device for uplink transmission in
an unlicensed band includes a transceiver to transmit and receive a
radio signal and a processor coupled to the transceiver. The
processor is configured to receive, via the transceiver, an uplink
grant for uplink transmission in an unlicensed band from a base
station (BS) through the transceiver, determine a delay time to
initiate clear channel assessment (CCA) from reference time, check,
via the transceiver, whether a channel is idle by performing CCA
for CCA duration after the delay time from the reference time, and
perform, via the transceiver, uplink transmission based on the
uplink grant when the channel is idle.
[0013] In an environment where various communication protocols
co-exist in an unlicensed band, deteriorating data reception
quality can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows an example of an LTE service using an
unlicensed band.
[0015] FIG. 2 shows an illustrative arrangement of a wireless
communication system.
[0016] FIG. 3 shows a communication method according to an
embodiment of the present invention.
[0017] FIG. 4 shows a communication method according to another
embodiment of the present invention.
[0018] FIG. 5 shows a communication method according to still
another embodiment of the present invention.
[0019] FIG. 6 shows a method for uplink transmission according to
an embodiment of the present invention.
[0020] FIG. 7 shows a method for uplink transmission according to
another embodiment of the present invention.
[0021] FIG. 8 is a block diagram illustrating a wireless
communication system according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0022] A wireless device may be fixed or mobile, and may be
referred to as another terminology, such as a user equipment (UE),
a mobile station (MS), a mobile terminal (MT), a user terminal
(UT), a subscriber station (SS), a personal digital assistant
(PDA), a wireless modem, a handheld device, etc. The wireless
device may also be a device supporting only data communication such
as a machine-type communication (MTC) device.
[0023] A base station (BS) is generally a fixed station that
communicates with the wireless device, and may be referred to as
another terminology, such as an evolved-NodeB (eNB), a base
transceiver system (BTS), an access point, etc.
[0024] Hereinafter, it is described that the present invention is
applied according to a 3rd generation partnership project (3GPP)
long term evolution (LTE) based on 3GPP technical specification
(TS). However, this is for exemplary purposes only, and thus the
present invention is also applicable to various wireless
communication networks.
[0025] In a carrier aggregation (CA) environment or a dual
connectivity environment, the wireless device may be served by a
plurality of serving cells. Each serving cell may be defined with a
downlink (DL) component carrier (CC) or a pair of a DL CC and an
uplink (UL) CC.
[0026] The serving cell may be classified into a primary cell and a
secondary cell. The primary cell operates at a primary frequency,
and is a cell designated as the primary cell when an initial
network entry process is performed or when a network re-entry
process starts or in a handover process. The primary cell is also
called a reference cell. The secondary cell operates at a secondary
frequency. The secondary cell may be configured after an RRC
connection is established, and may be used to provide an additional
radio resource. At least one primary cell is configured always. The
secondary cell may be added/modified/released by using higher-layer
signaling (e.g., a radio resource control (RRC) message).
[0027] A cell index (CI) of the primary cell may be fixed. For
example, a lowest CI may be designated as a CI of the primary cell.
It is assumed hereinafter that the CI of the primary cell is 0 and
a CI of the secondary cell is allocated sequentially starting from
1.
[0028] FIG. 1 shows an example of an LTE service using an
unlicensed band.
[0029] A wireless device 130 establishes a connection with a 1st BS
110, and receives a service through a licensed band 150. For
traffic offloading, the wireless device 130 may receive a service
through an unlicensed band 160 with respect to a 2nd BS 120.
[0030] The 1st BS 110 is a BS supporting an LTE system, whereas the
2nd BS 120 may also support other communication protocols such as a
wireless local area network (WLAN) in addition to LTE. The 1st BS
110 and the 2nd BS 120 may be associated with a carrier aggregation
(CA) environment, and a specific cell of the 1st BS 110 may be a
primary cell. Alternatively, the 1st BS 110 and the 2nd BS 120 may
be associated with a dual connectivity environment, and a specific
cell of the 1st BS 110 may be a primary cell. In general, the 1st
BS 110 having the primary cell has wider coverage than the 2nd BS
120. The 1st BS 110 may be called a macro cell. The 2nd BS 120 may
be called a small cell, a femto cell, or a micro cell. The 1st BS
110 may operate the primary cell and zero or more secondary cells.
The 2nd BS 120 may operate one or more secondary cells. The
secondary cell may be activated/deactivated by an indication of the
primary cell.
[0031] The above description is for exemplary purposes only. The
1st BS 110 may correspond to the primary cell, and the 2nd BS 120
may correspond to the secondary cell, so that the cell can be
managed by one BS.
[0032] The licensed band is a band in which an exclusive use is
guaranteed to a specific communication protocol or a specific
provider.
[0033] The unlicensed band is a band in which various communication
protocols coexist and a shared use is guaranteed. The unlicensed
band may include 2.5 GHz and/or 5 GHz band used in a WLAN.
[0034] It is assumed in the unlicensed band that a channel is
occupied basically through contention between respective
communication nodes. Therefore, in communication in the unlicensed
band, it is required to confirm that signal transmission is not
achieved by other communication nodes by performing channel
sensing. For convenience, this is called a listen before talk
(LBT), and if it is determined that signal transmission is not
achieved by other communication nodes, this case is defined as
confirmation of clear channel assessment (CCA).
[0035] The LBT must be performed preferentially in order for a BS
or wireless device of an LTE system to have access to a channel in
the unlicensed band. Further, when the BS or wireless device of the
LTE system transmits a signal, an interference problem may occur
since other communication nodes such as the WLAN or the like also
perform the LBT. For example, in the WLAN, a CCA threshold is
defined as -62 dBm as to a non-WLAN signal and is defined as -82
dBm as to a WLAN signal. This means that interference may occur in
an LTE signal due to other WLAN devices when the LTE signal is
received with power less than or equal to -62 dBm.
[0036] Hereinafter, when it is said that `LBT is performed` or `CCA
is performed`, it implies that whether a channel is idle or is used
by another node is confirmed first and thereafter the channel is
accessed.
[0037] Hereinafter, the LTE and the WLAN are described for example
as a communication protocol used in the unlicensed band. This is
for exemplary purposes only, and thus it may also be said that a
1st communication protocol and a 2nd communication protocol are
used in the unlicensed band. ABS supports the LTE. A UE is a device
supporting the LTE.
[0038] Hereinafter, although it is described that downlink (DL)
transmission is based on transmission performed by a BS and uplink
(UL) transmission is based on transmission performed by a UE, the
DL transmission and the UL transmission may also be performed by a
transmission node or node group in a wireless network. The UE may
imply an individual node which exists for each user, and the BS may
imply a central node for transmitting/receiving and controlling
data for a plurality of individual nodes. From this perspective,
the term `BS` may be replaced with a DL node, and the term `UE` may
be replaced with a UL node.
[0039] Hereinafter, a cell (or a carrier) operating in an
unlicensed band is called an unlicensed cell or an unlicensed
carrier. A cell operating in a licensed band is called a licensed
cell or a licensed carrier.
[0040] FIG. 2 shows an illustrative arrangement of a wireless
communication system.
[0041] A service provider divides an area into sectors having
appropriate coverage, and a BS managing each sector communicates
with a UE belonging to the sector. It is possible to maximize
frequency reuse by minimizing interference between different
sectors and allowing simultaneous transmissions in neighboring
sectors, thus increasing overall system throughput.
[0042] Since it is difficult to adjust the coverage of the sectors
or to adjust the distance between BSs between a plurality of
service providers, simultaneous transmissions of traffic by
adjacent BSs belonging to different service providers may cause
serious interference.
[0043] Therefore, if simultaneous transmissions by BSs of the same
wireless service provider are allowed and simultaneous
transmissions by BSs of different wireless service providers are
avoided through an LBT operation, overall system performance may be
increased. Likewise, if simultaneous transmissions by UEs connected
to BSs of the same service provider are allowed and simultaneous
transmissions by UEs connected to BSs of different service
providers are avoided through an LBT operation, overall system
performance may be increased.
[0044] Hereinafter, a method for performing a radio channel access
operation based on LBT in an unlicensed band while increasing the
probability of simultaneous transmissions by nodes (for example,
BSs and UEs) belonging to the same group is proposed.
[0045] FIG. 3 shows a communication method according to an
embodiment of the present invention.
[0046] BS1 and BS2 are BSs belonging to a first group, and BS3 is a
BS belonging to a second group. The number of groups and the number
of BSs belonging to a group are provided only for illustrative
purposes.
[0047] A criterion for dividing BSs by group may be a wireless
service provider, a geographical characteristic, a frequency band,
or the like, without being limited thereto.
[0048] First, terms are defined as follows. [0049] t1 and t2:
Reference time for transmission or CCA. Reference time may be the
boundary between subframes boundary or the boundary between radio
frames. Reference time may be a point which is defined by a
specific pattern or at which channel occupation expires. [0050]
Tdefer: Delay time from the reference time to the start of CCA.
Tdeferl(t1) denotes Tdefer of a first group at t1. [0051] Td: CCA
duration for which CCA is performed.
[0052] According to one embodiment, the same delay time Tdefer is
defined for each group. A delay time may be a fixed value obtained
based on a group-specific parameter (for example, a group
identifier) or may be obtained based on a group-specific parameter
in a specific period or at every reference time. A delay time may
be defined randomly at every reference time.
[0053] Each BS performs CCA for CCA duration Td after a delay time
from each reference time, and may start DL transmission when
determining that a channel is not occupied.
[0054] BS1 and BS2 in the first group start CCA after the same
Tdeferl (t1) from t1. As a result of CCA, when a channel is idle,
BS1 and BS2 start DL transmission at t1+Tdefer1(t1)+Td. Since
Tdefer2(t1) is longer than Tdefer1(t1), BS3 in the second group,
which performs CCA from Tdefer2(t1), determines that the channel is
busy and waits for transmission.
[0055] In t2, Tdefer1(t2) is longer than Tdefer2 (t2). Thus, BS3 in
the second group may detect an idle channel to start
transmission.
[0056] Since BSs belonging to different groups start CCA from
different times, the BSs in the different groups can perform
transmissions, avoiding a collision between each other through an
LBT operation.
[0057] FIG. 4 shows a communication method according to another
embodiment of the present invention.
[0058] The same CCA duration Td is defined for each group. CCA
duration may be a fixed value obtained based on a group-specific
parameter (for example, a group identifier) or may be obtained
based on a group-specific parameter in a specific period or at
every reference time. CCA duration may be defined randomly at every
reference time.
[0059] Td1(t1) denotes Td of the first group in t1, and Td2(t1)
denotes Td of the second group in t1.
[0060] A BS may start CCA from t1, and may start transmission from
time t1+Td(t1) when determining that a channel is not occupied.
[0061] BS1 and BS2 in the first group perform CCA for the same
Td1(t1) from t1. As a result of CCA, when a channel is idle, BS1
and BS2 start DL transmission at t1+Td1(t1). Since Td2(t1) is
longer than Td1(t1), BS3 in the second group, which performs CCA
for Td2(t1), determines that the channel is busy and waits for
transmission.
[0062] In t2, Td1(t2) is longer than Td2(t2). Thus, BS3 in the
second group may detect an idle channel for Td2(t2) and may start
transmission.
[0063] Since BSs belonging to different groups have different
lengths of CCA duration, the BSs in the different groups can
perform transmissions, avoiding a collision between each other
through an LBT operation.
[0064] FIG. 5 shows a communication method according to still
another embodiment of the present invention.
[0065] Different lengths of CCA duration are defined at reference
time t1 for BSs belonging to the same group, and a delay time is
defined in inverse proportion to CCA duration. A transmission start
time T is a time for actually starting transmission after CCA is
finished.
[0066] In t1, CCA duration Td1(t1) is defined for BS1 and Td2(t1)
is defined for BS2. A delay time for deferring the start of CCA is
Tdefer1(t1)=T-Td1(t1) for BS1 and is Tdefer2(t1)=T-Td2(t1) for BS2.
When a channel is not occupied from t1 to t+T, both BS1 and BS2 can
start transmission at t+T.
[0067] Different transmission start times T may be set for
different groups in order to prevent BSs in the different groups
from simultaneously starting transmission.
[0068] Information on a pattern for reference time (the cycle of
reference time/offset) may be shared among BSs in the same group.
The BSs may provide a UE with the information on the pattern.
[0069] Information on parameters for determining a delay time, CCA
duration, and/or transmission start time may be shared among BSs in
same group. The BSs may provide a UE with the information on the
parameters.
[0070] The foregoing embodiments for frequency reuse relate to BSs
belonging to different groups. These embodiments may also be
applied to UEs belonging to different groups.
[0071] FIG. 6 shows a method for uplink transmission according to
an embodiment of the present invention.
[0072] UE1 and UE2 belong to a first group, and UE3 belongs to a
second group. A criterion for dividing UEs by group may be a
wireless service provider, a geographical characteristic, a
frequency band, or the like, without being limited thereto.
Specifically, the first group may include a UE connected to a BS
operated by a first service provider, and the second group may
include a UE connected to a BS operated by a second service
provider.
[0073] A plurality of groups may trigger uplink transmissions at
the same reference time. Suppose that UE1 and UE2 in the first
group receive a first UL grant and UE2 in the second group receives
a second UL grant. A separate UL grant may be given for each UE, or
UL transmissions by a plurality of UEs may be triggered by a single
UL grant.
[0074] Reference time t1 is a point at which CCA for UL
transmission may be started upon receiving a UL grant.
[0075] The same delay time Tdefer is defined for each group. A
delay time may be a fixed value obtained based on a group-specific
parameter (for example, a group identifier) or may be obtained
based on a group-specific parameter in a specific period or at
every reference time. A delay time may be defined randomly at every
reference time. A UL grant for each group may include information
on parameters used to determine a corresponding delay time.
[0076] Each UE performs CCA for CCA duration Td after a delay time
from each reference time, and may start UL transmission when
determining that a channel is not occupied.
[0077] UE1 and UE2 in the first group start CCA after the same
Tdeferl (t1) from t1. As a result of CCA, when a channel is idle,
UE1 and UE2 start UL transmission at t1+Tdefer1(t1)+Td. Since
Tdefer2(t1) is longer than Tdefer1(t1), UE3 in the second group,
which performs CCA from Tdefer2(t1), determines that the channel is
busy and waits for transmission.
[0078] FIG. 7 shows a method for uplink transmission according to
another embodiment of the present invention.
[0079] The same CCA duration Td is defined for each group. CCA
duration may be a fixed value obtained based on a group-specific
parameter (for example, a group identifier) or may be obtained
based on a group-specific parameter in a specific period or at
every reference time. CCA duration may be defined randomly at every
reference time. A UL grant for each group may include information
on parameters used to determine corresponding CCA duration.
[0080] Td1(t1) denotes Td of the first group in t1, and Td2(t1)
denotes Td of the second group in t1.
[0081] A UE may start CCA from t1, and may start transmission from
time t1+Td(t1) when determining that a channel is not occupied.
[0082] UE1 and UE2 in the first group perform CCA for the same
Td1(t1) from t1. As a result of CCA, when a channel is idle, UE1
and UE2 start UL transmission at t1+Td1(t1). Since Td2(t1) is
longer than Td1(t1), UE3 in the second group, which performs CCA
for Td2(t1), determines that the channel is busy and waits for
transmission.
[0083] FIG. 8 is a block diagram illustrating a wireless
communication system according to an embodiment of the present
invention.
[0084] A wireless device 50 includes a processor 51, a memory 52,
and a transceiver 53. The memory 52 is coupled to the processor 51
and stores various instructions that are executed by the processor
51. The transceiver 53 is coupled to the processor 51 and transmits
and/or receives radio signals. The processor 51 implements the
proposed functions, processes and/or methods. In the embodiments
described above, an operation of a UE may be implemented by the
processor 51. When the above-described embodiments are implemented
by software instructions, the instructions may be stored in the
memory 52 and may be executed by the processor 51, thereby
performing the operations described above.
[0085] A BS 60 includes a processor 61, a memory 62, and a
transceiver 63. The BS 60 may operate in an unlicensed band. The
memory 62 is coupled to the processor 61 and stores various
instructions that are executed by the processor 61. The transceiver
63 is coupled to the processor 61 and transmits and/or receives
radio signals. The processor 61 implements the proposed functions,
processes and/or methods. In the embodiments described above, an
operation of a BS may be implemented by the processor 61.
[0086] The processor may include Application-Specific Integrated
Circuits (ASICs), other chipsets, logic circuits, and/or data
processors. The memory may include Read-Only Memory (ROM), Random
Access Memory (RAM), flash memory, memory cards, storage media
and/or other storage devices. The RF unit may include a baseband
circuit for processing a radio signal. When the above-described
embodiment is implemented in software, the above-described scheme
may be implemented using a module (process or function) which
performs the above function. The module may be stored in the memory
and executed by the processor. The memory may be disposed to the
processor internally or externally and connected to the processor
using a variety of well-known means.
[0087] In the above exemplary systems, although the methods have
been described on the basis of the flowcharts using a series of the
steps or blocks, the present invention is not limited to the
sequence of the steps, and some of the steps may be performed at
different sequences from the remaining steps or may be performed
simultaneously with the remaining steps. Furthermore, those skilled
in the art will understand that the steps shown in the flowcharts
are not exclusive and may include other steps or one or more steps
of the flowcharts may be deleted without affecting the scope of the
present invention.
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