U.S. patent application number 16/504981 was filed with the patent office on 2019-10-31 for method and apparatus for uplink channel accessing wireless communication system.
The applicant listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Taehan BAE, Seunghoon CHOI, Jinyoung OH, Jeongho YEO.
Application Number | 20190335433 16/504981 |
Document ID | / |
Family ID | 59722405 |
Filed Date | 2019-10-31 |
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United States Patent
Application |
20190335433 |
Kind Code |
A1 |
OH; Jinyoung ; et
al. |
October 31, 2019 |
METHOD AND APPARATUS FOR UPLINK CHANNEL ACCESSING WIRELESS
COMMUNICATION SYSTEM
Abstract
A communication technique for fusing 5G communication, which
supports a higher data transmission rate than a 4G system, with an
IoT technology is provided, and may be applied to an intelligent
service based on the 5G communication technology and the IoT
related technology. Accordingly, a method for transmitting
information by a base station in a wireless communication system,
includes generating information on a channel sensing operation of a
user equipment (UE) in an unlicensed band, wherein the information
on the channel sensing operation indicates one of a first type
performing the channel sensing operation using a variable time
period, a second type performing the channel sensing operation
using a fixed time period, and a third type not performing the
channel sensing operation; and transmitting, to the UE, the
information on the channel sensing operation.
Inventors: |
OH; Jinyoung; (Seoul,
KR) ; YEO; Jeongho; (Gyeonggi-do, KR) ; BAE;
Taehan; (Seoul, KR) ; CHOI; Seunghoon;
(Gyeonggi-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Gyeonggi-do |
|
KR |
|
|
Family ID: |
59722405 |
Appl. No.: |
16/504981 |
Filed: |
July 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15448218 |
Mar 2, 2017 |
10349392 |
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16504981 |
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62302489 |
Mar 2, 2016 |
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62373521 |
Aug 11, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 74/0816 20130101;
H04W 74/085 20130101; H04W 72/042 20130101; H04W 74/0808
20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04W 74/08 20060101 H04W074/08 |
Claims
1. A base station for transmitting information in a wireless
communication system, the base station comprising: a transceiver;
and a controller coupled with the transceiver and configured to
control to: generate information on a channel sensing operation of
a user equipment (UE) in an unlicensed band, wherein the
information on the channel sensing operation indicates one of a
first type performing the channel sensing operation using a
variable time period, a second type performing the channel sensing
operation using a fixed time period, and a third type not
performing the channel sensing operation, and transmit, to the UE,
the information on the channel sensing operation.
2. The base station of claim 1, wherein the information on the
channel sensing operation indicates the third type in case that a
gap from an end of a downlink (DL) transmission to a beginning of a
uplink (UL) transmission is not greater than a predetermined
time.
3. The base station of claim 1, wherein an uplink signal is
transmitted after sensing a channel for the unlicensed band during
the variable time period in case that the information on the
channel sensing operation indicates the first type, and wherein the
uplink signal is transmitted after sensing the channel for the
unlicensed band during the fixed time period in case that the
information on the channel sensing operation indicates the second
type.
4. The base station of claim 1, wherein the variable time period
for the first type is randomly selected based on a contention
window for the UE.
5. The base station of claim 4, wherein a value of the contention
window is determined based on a new data indicator (NDI) value for
a hybrid automatic repeat request (HARQ) process.
6. A method for transmitting information by a base station in a
wireless communication system, the method comprising: generating
information on a channel sensing operation of a user equipment (UE)
in an unlicensed band, wherein the information on the channel
sensing operation indicates one of a first type performing the
channel sensing operation using a variable time period, a second
type performing the channel sensing operation using a fixed time
period, and a third type not performing the channel sensing
operation; and transmitting, to the UE, the information on the
channel sensing operation.
7. The method of claim 6, wherein the information on the channel
sensing operation indicates the third type in case that a gap from
an end of a downlink (DL) transmission to a beginning of a uplink
(UL) transmission is not greater than a predetermined time.
8. The method of claim 6, wherein an uplink signal is transmitted
after sensing a channel for the unlicensed band during the variable
time period in case that the information on the channel sensing
operation indicates the first type, and wherein the uplink signal
is transmitted after sensing the channel for the unlicensed band
during the fixed time period in case that the information on the
channel sensing operation indicates the second type.
9. The method of claim 6, wherein the variable time period for the
first type is randomly selected based on a contention window for
the UE.
10. The method of claim 9, wherein a value of the contention window
is determined based on a new data indicator (NDI) value for a
hybrid automatic repeat request (HARQ) process.
11. A user equipment (UE) for receiving information in a wireless
communication system, the UE comprising: a transceiver; and a
controller coupled with the transceiver and configured to control
to: receive, from a base station, information on a channel sensing
operation of the UE in an unlicensed band, wherein the information
on the channel sensing operation indicates one of a first type
performing the channel sensing operation using a variable time
period, a second type performing the channel sensing operation
using a fixed time period, and a third type not performing the
channel sensing operation, and transmit an uplink signal based on
the information on the channel sensing operation.
12. The UE of claim 11, wherein the information on the channel
sensing operation indicates the third type in case that a gap from
an end of a downlink (DL) transmission to a beginning of a uplink
(UL) transmission is not greater than a predetermined time.
13. The UE of claim 11, wherein the controller is configured to:
transmit the uplink signal after sensing a channel for the
unlicensed band during the variable time period in case that the
information on the channel sensing operation indicates the first
type, and transmit the uplink signal after sensing the channel for
the unlicensed band during the fixed time period in case that the
information on the channel sensing operation indicates the second
type.
14. The UE of claim 11, wherein the variable time period for the
first type is randomly selected based on a contention window for
the UE.
15. The UE of claim 14, wherein a value of the contention window is
determined based on a new data indicator (NDI) value for a hybrid
automatic repeat request (HARQ) process.
16. A method for receiving information by a user equipment (UE) in
a wireless communication system, the method comprising: receiving,
from a base station, information on a channel sensing operation of
the UE in an unlicensed band, wherein the information on the
channel sensing operation indicates one of a first type performing
the channel sensing operation using a variable time period, a
second type performing the channel sensing operation using a fixed
time period, and a third type not performing the channel sensing
operation; and transmitting an uplink signal based on the
information on the channel sensing operation.
17. The method of claim 16, wherein the information on the channel
sensing operation indicates the third type in case that a gap from
an end of a downlink (DL) transmission to a beginning of a uplink
(UL) transmission is not greater than a predetermined time.
18. The method of claim 16, further comprising: transmitting the
uplink signal after sensing a channel for the unlicensed band
during the variable time period in case that the information on the
channel sensing operation indicates the first type; and
transmitting the uplink signal after sensing the channel for the
unlicensed band during the fixed time period in case that the
information on the channel sensing operation indicates the second
type.
19. The method of claim 16, wherein the variable time period for
the first type is randomly selected based on a contention window
for the UE.
20. The method of claim 19, wherein a value of the contention
window is determined based on a new data indicator (NDI) value for
a hybrid automatic repeat request (HARQ) process.
Description
PRIORITY
[0001] This application is a Continuation Application of U.S.
patent application Ser. No. 15/448,218, which was filed in the U.S.
Patent and Trademark Office on Mar. 2, 2017, and claims priority
under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Application Ser.
No. 62/302,489, which was filed on Mar. 2, 2016, and to U.S.
Provisional Application Ser. No. 62/373,521, which was filed on
Aug. 11, 2016, the entire disclosure of each of these applications
is incorporated herein by reference.
BACKGROUND
1. Field of the Disclosure
[0002] The present disclosure relates to a channel sensing method,
and more particularly, to a channel access method including a
channel sensing operation and a channel occupation operation that
are performed by a transmitting node or a receiving node for uplink
signal transmission in a wireless communication system using an
unlicensed band.
2. Description of the Related Art
[0003] To meet a demand for radio data traffic that is on an
increasing trend since commercialization of a 4G communication
system, efforts to develop an improved 5G communication system or a
pre-5G communication system have been conducted. For this reason,
5G communication systems or the pre-5G communication systems can be
called a beyond 4G network communication system or a post LTE
system.
[0004] To achieve a high data transmission rate, the 5G
communication system is considered to be implemented in a super
high frequency (mmWave) band (e.g., a 60 GHz band). To relieve a
path loss of a radio wave and increase a transfer distance of a
radio wave in the super high frequency band, in the 5G
communication system, technologies such as beamforming, massive
multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO),
an array antenna, analog beam-forming, and a large scale antenna
have been used. Further, to improve a network of the system, in the
5G communication system, technologies such as an evolved small
cell, an advanced small cell, a cloud radio access network (RAN),
an ultra-dense network, a device to device communication (D2D), a
wireless backhaul, a moving network, cooperative communication,
coordinated multi-points (CoMP), and interference cancellation have
been developed. In addition, in the 5G system, hybrid frequency
shift keying (FSK) and quadrature amplitude modulation (QAM)
modulation (FQAM) and sliding window superposition coding (SWSC),
which are an advanced coding modulation (ACM) scheme and a filter
bank multi carrier (FBMC), a non-orthogonal multiple access (NOMA),
and a sparse code multiple access (SCMA) that are an advanced
access technology, and so on have been developed.
[0005] Meanwhile, the Internet has evolved from in a human-centered
connection network through which a human being generates and
consumes information to an internet of things (IoT) network that
transmits and receives information between distributed components
such as things and processes the information. The internet of
everything (IoE) technology in which the big data processing
technology is combined with the IoT technology by connection with a
cloud server has also emerged. To implement the IoT, technology
elements, such as a sensing technology, wired and wireless
communication and network infrastructure, a service interface
technology, and a security technology, have been required.
Recently, technologies such as a sensor network, machine to machine
(M2M), and machine type communication (MTC) for connecting between
things has been researched. In the IoT environment, an intelligent
internet technology (IT) service that creates a new value in human
life by collecting and analyzing data generated in the connected
things may be provided. The IoT may be applied to fields, such as a
smart home, a smart building, a smart city, a smart car or a
connected car, a smart grid, health care, smart appliances, and an
advanced healthcare service, by fusing and combining the existing
information technology with various industries.
[0006] Therefore, various attempts to apply the 5G communication
system to the IoT network have been conducted. For example, the 5G
communication technologies, such as the sensor network, the M2M,
and the MTC, have been implemented by techniques such as
beamforming, MIMO, and the array antenna. An example of the
application of the cloud radio access network (cloud RAN) as the
big data processing technology described above may also be the
fusing of 5G technology with the IoT technology.
[0007] To meet a demand for wireless data traffic, discussions are
underway to develop communication methods in various fields. For
example, there are user equipment (UE) to UE communication, a
frequency integration system for operating a plurality of cells,
and a multi-antenna system using a large-scale antenna, or the
like.
[0008] In recent years, a wireless communication system has been
developed as a high-speed and high-quality wireless packet data
communication system to provide a data service and a multimedia
service in addition to provision of early voice-oriented service.
In order to support the high-speed and high quality wireless packet
data transmission service, various wireless communication standards
such as high speed downlink packet access (HSDPA), high speed
uplink packet access (HSUPA), long term evolution (LTE), long term
evolution advanced (LTE-A) of 3rd generation partnership project
(3GPP), high rate packet data (HRPD) of 3GPP2, and 802.16 of
Institute of Electrical and Electronics Engineers (IEEE) have been
developed. In particular, the LTE/LTE-A (LTE) has been continuously
developed and progressed to improve system throughput and frequency
efficiency. Typically, in the case of the LTE system, data
transmission rate and system throughput may be significantly
increased by using a frequency integration technology (carrier
aggregation, (CA)) capable of operating the system using a
plurality of frequency spectra. However, the frequency spectrum in
which the LTE system currently operates is a licensed band or
licensed carrier that an operator may use with its own authority.
When a frequency spectrum (e.g., 5 GHz or less) in which the
wireless communication service is typically provided, since it is
already occupied and used by other operators or other communication
systems, it may be difficult for the operator to secure a plurality
of licensed band frequencies. Therefore, it is difficult to
increase the system throughput using the CA technology.
Accordingly, in order to process increasing mobile data in a
situation in which it is hard to secure the licensed band frequency
as described above, recently, a technology for utilizing the LTE
system in an unlicensed band or unlicensed carrier has been
researched (e.g., LTE in unlicensed (LTE-U) and licensed-assisted
access (LAA)). Among the unlicensed spectra, particularly, 5 GHz
spectrum is used by the relatively smaller number of communication
devices as compared to 2.4 GHz unlicensed band, and may utilize
significantly wide bandwidth, thus it is relatively easy to secure
additional frequency spectrum. In other words, the licensed band
frequency and the unlicensed band frequency may be utilized by
using the LTE technology aggregating and using a plurality of
frequency spectra, that is, the CA technology. In other words, an
LTE cell in a licensed band may be set as PCell (or Pcell), an LTE
in an unlicensed band (LAA cell or LTE-U cell) may be set as SCell
(or Scell), such that the LTE system may be operated in the
licensed band and the unlicensed band using the existing CA
technology. The system may also be applied to a dual-connectivity
environment, in which the licensed band and the unlicensed band are
connected by a non-ideal backhaul, as well as the CA, in which the
licensed band and the unlicensed band are connected by an ideal
backhaul. However, in the present disclosure, the description will
be made under the assumption of the CA environment in which the
licensed band and the unlicensed band are connected by an ideal
backhaul.
[0009] Generally, the LTE/LTE-A system is a method of transmitting
data by using an orthogonal frequency division multiple access
(OFDM) transmission scheme. In the OFDM scheme, a modulation signal
is positioned at a two-dimensional resource configured of a time
and a frequency. Resources on a time-axis are distinguished from
each other by different OFDM symbols, and are orthogonal to each
other. Resources on a frequency-axis are distinguished from each
other by different sub-carriers, and are also orthogonal to each
other. That is, in the OFDM scheme, when a specific OFDM symbol on
the time-axis is designated and a specific sub-carrier on the
frequency-axis is designated, one minimum unit resource may be
indicated. The indicated minimum unit resource can be referred to
as a resource element (RE). Different REs are orthogonal to each
other even after passing through a frequency selective channel,
therefore signals transmitted through different REs may be received
by a reception side without causing interference with each other.
In the OFDM communication system, a downlink bandwidth includes a
plurality of resource blocks (RB), and each physical resource block
(PRB) may include 12 sub-carriers arranged along the frequency-axis
and 14 or 12 OFDM symbols arranged along the time-axis. Here, the
PRB can be a basic unit for resource allocation.
[0010] A reference signal (RS) that is received from a base
station, is a signal allowing a terminal to estimate a channel. In
an LTE communication system, a demodulation reference signal (DMRS)
can be included as one of a common reference signal (CRS) and an
exclusive reference signal. A CRS that is a reference signal
transmitted across entire downlink bandwidth, may be received by
all terminals, and can be used in channel estimation, feedback
information configuration of the terminal, or demodulation of a
control channel and a data channel. A DMRS that is also a reference
signal transmitted across entire downlink bandwidth, can be used in
data channel modulation and channel estimation of a specific
terminal, but is not used in feedback information configuration,
unlike the CRS. Therefore, The DMRS can be transmitted through the
PRB resource to be scheduled by the terminal.
[0011] On the time-axis, a subframe includes two slots, a first
slot and a second slot, each having a length of 0.5 msec. A
physical dedicated control channel (PDCCH) region that is a control
channel region and an enhanced PDCCH (ePDCCH) region that is a data
channel region are divided on the time-axis and then transmitted.
This is to rapidly receive and demodulate the control channel
signal. In addition, the PDCCH region is positioned across the
entire downlink spectrum and has a form in which one control
channel is divided into small units of control channels to be
dispersed in the entire downlink spectrum. An uplink is largely
divided into a control channel (PUCCH) and a data channel (PUSCH),
and a response channel for the downlink data channel and other
feedback information are transmitted through the control channel
when the data channel is not present, and are transmitted through
the data channel when the data channel is present.
[0012] FIGS. 1A and 1B are diagrams illustrating a conventional
communication system to which the present disclosure can be
applied.
[0013] Referring to FIGS. 1A and 1B, FIG. 1A illustrates a case in
which an LTE cell 102 and an LAA cell 103 coexist in one small base
station 101 in a network, and a terminal 104 performs transmission
and reception of data with the base station 101 through the LTE
cell 102 and the LAA cell 103. Schemes other than a duplex scheme
of the LTE cell 102 or the LAA cell 103 can also be used. A cell
performing data transmission and data reception by using a licensed
band may be assumed as the LTE cell 102 or PCell, and a cell
performing data transmission and data reception by using an
unlicensed band may be assumed as the LAA cell 103 or SCell.
However, when the LTE cell is PCell, uplink transmission may be
performed only through the LTE cell 102.
[0014] FIG. 1B illustrates a case in which an LTE macro base
station 111 for achieving wide coverage in the network and an LAA
small base station 112 for increasing data transmission amount are
installed; schemes other than a duplex scheme of the LTE macro base
station 111 or the LAA small base station may also be used. In this
case, the LTE macro base station 111 may also be replaced by an LTE
small base station. Further, when the LTE base station is PCell,
uplink transmission may be performed only through the LTE base
station 111. The LTE base station 111 and the LAA base station 112
can be assumed to have an ideal backhaul network. Accordingly, fast
X2 communication (or interface) 113 between the base stations is
possible, such that even when the uplink transmission is performed
only through the LTE base station 111, the LAA base station 112 may
receive relevant control information from the LTE base station 111
through the X2 communication 113 in real time. Methods in
accordance with the present disclosure may be applied to both of
the systems in FIG. 1A and FIG. 1B.
[0015] In general, the unlicensed band is used in a manner that a
plurality of devices share the same frequency spectrum or channel.
The devices using the unlicensed band may be systems different from
each other. Therefore, general operation of the devices operated in
the unlicensed band for coexistence of various devices is as
follows.
[0016] A transmitting device requiring transmission of a signal
including a data signal, a control signal, or the like, confirms,
with respect to the unlicensed band or a channel in which the
signal transmission is performed, channel occupancy state of other
devices before performing the signal transmission, and may occupy
the channel depending on the determined channel occupancy state.
The operation as described above is generally called
listen-before-talk (LBT). In other words, the transmitting device
needs to determine whether the transmitting device may occupy the
channel according to a predefined or preset method. A method for
sensing the channel may be defined or set in advance. Further, the
time for sensing the channel may be defined or set in advance or
randomly selected within a specific range. Moreover, the channel
sensing time may be set in proportion to a set maximum channel
occupancy time. A channel sensing operation for determining whether
the channel may be occupied as described above may be set to be
different depending on an unlicensed frequency spectrum in which
the operation is performed, or regional and national regulation.
For example, currently, in the United States, the unlicensed band
may be used without a separate channel sensing operation except an
operation for radar sensing in a frequency spectrum of 5 GHz.
[0017] The transmitting devices to use the unlicensed band may
sense whether other devices use the corresponding channel through
the foregoing channel sensing operation (or LBT) as described
above, and use the channel by occupying the channel when it is
sensed that the channel is not occupied by other devices in the
channel. The devices using the unlicensed band may operate by
defming or setting a maximum channel occupancy time for which the
devices may continuously occupy a channel after the channel sensing
operation, in advance. The maximum channel occupancy time may be
defined in advance according to regulation defined in accordance
with a frequency spectrum, a region, or the like, or may be
separately set by a base station in a case of other devices, e.g.,
a terminal. The channel occupancy time may be set to be different
depending on an unlicensed band or regional and national
regulations. For example, in Japan, the maximum channel occupancy
time is set to 4 ms in the unlicensed band of 5 GHz. Meanwhile, in
Europe, the continuous channel occupancy time may be set to 10 ms
or 13 ms. The devices occupying the channel for the maximum channel
occupancy time may perform the channel sensing operation again, and
then reoccupy the channel according to the channel sensing
result.
[0018] The channel sensing operation and the channel occupation
operation in the unlicensed band as described above will be
described below with reference to FIG. 2, which illustrates a
downlink transmission process of transmitting, by the base station,
data or control signal to the terminal as an example, and the
process may also be applied to uplink transmission in which the
terminal transmits a signal to the base station.
[0019] An LTE subframe 200 in FIG. 2 is a subframe having a length
of 1 ms, and may be configured of a plurality of OFDM symbols. The
base station and the terminal capable of performing communication
using an unlicensed band may perform communication by occupying a
corresponding channel during a set channel occupancy time 250 and
260. When the base station occupying the channel for the set
channel occupancy time 250 needs to additionally occupy the
channel, the base station may perform the channel sensing operation
220, and then may reoccupy and use the channel depending on a
result of the channel sensing operation. The required channel
sensing period (or length) may be defined between the base station
and the terminal in advance, set through a higher layer signal
transmitted by the base station for the terminal, or set to be
different according to a transmission/reception result of data
transmitted through the unlicensed band.
[0020] Further, at least one of variables applied to the channel
sensing operation that is performed again as described above may be
set to be different from those of the previous channel sensing
operation.
[0021] The operation for sensing and occupying a channel may be set
to be different depending on the unlicensed band or regional and
national regulations. The operation for sensing and occupying a
channel with respect to a load-based equipment, which is one of
channel access methods in EN301 893, a rule for 5 GHz spectrum of
Europe, will be described in more detail below.
[0022] When the base station needs to additionally use the channel
after the maximum channel occupancy time 250, it is required to
determine whether other devices occupy the channel during a minimum
channel sensing period 220. The minimum channel sensing period 220
may be set with a, depending on the maximum channel occupancy
period, maximum channel occupancy period of 13/32.times.q, (q=4, .
. . , 32) and a minimum channel sensing period of length of
extended clear channel assessment (ECCA) slot x rand (1, q).
[0023] Here, the length of the ECCA slot is a predefined or preset
minimum unit (or length) of the channel sensing period. That is,
when q is set to 32, the transmitting device may occupy the
unlicensed band for up to 13 ms. A minimum channel sensing period,
a random value from 1 to q (that is, 1 to 32), may be selected, and
a total channel sensing period may be the length of the ECCA slot x
of the selected random value. Therefore, when the maximum channel
occupancy period is increased, the minimum channel sensing period
can also be increased. The method for setting the maximum channel
occupancy period and the minimum channel sensing period is merely
an example, may be applied differently depending on the frequency
spectrum, and the defined regional and national regulations, and
may be changed depending on frequency regulation amendments still
to be determined. Further, an additional operation (e.g.,
introduction of additional channel sensing period) in addition to
the channel sensing operation according to the frequency regulation
may also be included.
[0024] When other devices using the corresponding unlicensed band
is not sensed by the base station in the channel sensing period
220, that is, when the channel is determined to be in an idle
state, the base station may immediately occupy and use the channel.
The determination on whether other devices occupy the channel in
the channel sensing period 220 may be performed using a predefined
or preset reference value. For example, when intensity of a signal
received from other devices during the channel sensing period is
greater than a predetermined reference value (e.g., -62 dBm), it
may be determined that the channel is occupied by other devices.
When the intensity of the received signal is smaller than a
reference value, the channel may be determined to be in the idle
state. The method for determining whether the channel is occupied
may include various methods such as the foregoing method using the
size of the reception signal, a method of detecting a signal
defined in advance, or the like.
[0025] Since a general LTE operation is performed in a subframe
unit, the signal may not be transmitted or received in the specific
OFDM symbol immediately after performing the channel sensing
operation (e.g., a signal transmission and reception operation is
performed from a first OFDM symbol of the subframe). Therefore, the
base station sensing the idle channel in the channel sensing period
220 in the subframe as described above may transmit a specific
signal 230 for channel occupancy from the point in time when the
channel sensing period 220 ends to immediately before first OFDM
symbol transmission of a next subframe, i.e., during a period 230.
In other words, the base station may transmit a second signal
(e.g., primary synchronization signal (PSS)/secondary
synchronization signal (SSS)/cell-specific reference signal (CRS),
a newly defined signal, etc.) for channel occupancy with respect to
corresponding unlicensed band, synchronization of the terminal,
etc., before transmitting a first signal (e.g., general ePDCCH and
PDSCH) transmitted in the subframe 210 or 240. The transmitted
second signal may not be transmitted depending on the channel
sensing period ending point in time. Further, when a corresponding
channel occupancy starting point in time is set within the specific
OFDM symbol, a third signal (a newly defined signal) is transmitted
to a next OFDM symbol starting point in time, and the second signal
or the first signal may be transmitted. In the present disclosure,
the channel sensing operation period is described using an OFDM
symbol unit, but the channel sensing operation period may be set
regardless of the OFDM symbol of the LTE system.
[0026] Here, the PSS/SSS currently used in the LTE system may be
reused as the second signal, or the second signal may be generated
using at least one of the PSS and the SSS by using root sequence
currently used in the licensed band and other sequence. Further,
the second signal may be generated using other sequences except the
PSS/SSS sequence required to generate a physical cell ID (PCID) of
the base station in the unlicensed band to be used without being
confused with the physical cell ID of the base station. Further,
the second signal includes at least one of CRS and CSI-RS currently
used in the LTE system, or ePDCCH, PDSCH, or a signal having
modified form of ePDCCH and PDSCH may be used as the second
signal.
[0027] Since the period 230 in which the second signal is
transmitted is included in the channel occupancy time, frequency
efficiency may be maximized by allowing minimum information to be
transmitted through the second signal transmitted in the period
230.
[0028] The LTE system (LAA or LAA cell) using the unlicensed band
as described above requires a new channel access (or LBT) scheme
that is different from the existing method of using the licensed
band, in order to satisfy regulations on the unlicensed band to be
used and coexist with other systems (wireless-fidelity (WiFi))
using the unlicensed band.
[0029] Referring to FIG. 3, the channel access scheme for using the
unlicensed band of the WiFi system is now described.
[0030] When a WiFi AP1 310 has data to be transmitted to station 1
(STA1) or a terminal 1 315, a channel sensing operation for a
corresponding channel can be performed to occupy the channel.
Generally the channel is sensed during distributed coordination
function (DCF) interframe space (DIFS) time 330. Whether the
channel is occupied by other devices may be determined by various
methods, e.g., using intensity of the signal received during the
time 330, a method of detecting a signal defined in advance, or the
like. When it is determined that the channel is occupied by another
device 320 during the channel sensing time 330, the AP1 310 selects
a random variable 355, e.g., N in a set contention window (e.g.,
1-16). Generally, such operation is called a backoff operation.
Then, the AP1 310 senses the channel during a predefined time
(e.g., 9 us), and when it is determined that the channel is in the
idle state, the selected variable N 355 can be subtracted by 1.
That is, it is updated as N=N-1. When it is determined that the
channel is occupied by the another device 320 during the time 330,
the variable N 355 is not subtracted but is instead frozen. STA2
325 receives data 340 transmitted by the AP2 320 and transmits ACK
or NACK 347 with respect to the reception of the data 340 to the
AP2 320 after short interframe space (SIFS) time 345. The STA2 325
may transmit the ACK/NACK 347 without performing a separate channel
sensing operation. After the transmission of the ACK 347 of the
STA2 325 ends, the AP1 310 may know that the channel is in the idle
state. The API 310 senses the channel during a predetermined time
(e.g., 9 us) defined or set in advance for the backoff operation
when it is determined that the channel is in the idle state for the
DIFS time 350, and when it is determined that the channel is in the
idle state, the selected variable N 355 is subtracted again. That
is, it is updated as N=N-1. When N=0, the AP1 310 may occupy the
channel to transmit the data 360 to the STA 1 315. Then, the
terminal receiving the data 360 may transmit the ACK or NACK with
respect to the reception of the data to the AP1 310 after the SIFS
time. The AP1 310 receiving the NACK from the STA1 315 may select
the random variable N used in the next backoff operation in the
increased contention window. That is, when it is assumed that the
contention window used is [1, 16], and the data reception result of
the STA1 315 is NACK, the contention window of the AP1 310
receiving the NACK may be increased to [1, 32]. If the AP1 310
receives ACK in the above case, the contention window may be set to
an initial value (e.g., [1, 16]) or a preset contention window may
be decreased or maintained.
[0031] However, with a WiFi system, communication is generally
performed between one AP (or base station) and one STA (or
terminal) at the same time. Further, as 347 and 370 in FIG. 3, the
STA1 and STA2 (or terminals 315, 325) transmits its data reception
state (e.g., ACK or NACK) to the AP (or base station) immediately
after the reception of the data. The AP 310 or 320 performs a
channel sensing operation for the next data transmission operation
after receiving ACK or NACK from the terminal 315 or 325. However,
in the LAA system, one base station may transmit data to a
plurality of terminals at the same time. Further, one or more
terminals receiving the data at the same point in time (e.g., time
n) may transmit ACK or NACK to the base station at the same time
(e.g., n+4 in a case of FDD). Therefore, the LAA base station may
receive the ACK or NACK from one or more terminals at the same
point in time, unlike the WiFi system. In addition, time difference
between the ACK/NACK transmission point in time of the terminal and
the data transmission time of the base station may be at least 4
ms. Therefore, of the LAA base station sets (or resets) a
contention window by the ACK/NACK received from the terminal like
WiFi, since the base station may receive the ACK/NACK from a
plurality of terminals at a specific time, uncertainty in setting
the contention window may occur. Further, if the terminal performs
an uplink channel sensing operation for uplink transmission, each
terminal may independently perform the channel sensing operation.
When the terminal independently performs the channel sensing
operation as described above, only a terminal of which the channel
sensing operation ends first may perform the set uplink
transmission.
[0032] Accordingly, the present disclosure provides a method in
which the base station sets a channel sensing period based on the
uplink signal reception result received from the terminal, and
performs a setting of the set channel sensing period for terminals
such that the plurality of terminals may perform the channel
sensing operation at the same time.
SUMMARY
[0033] Accordingly, an aspect of the present disclosure provides a
method and an apparatus for setting a channel sensing period for an
unlicensed band.
[0034] An aspect of the present disclosure provides that when
performing a channel occupation operation in an unlicensed band, at
least one of variables for the channel occupation operation is set
by using a data reception result transmitted using the unlicensed
band.
[0035] In accordance with an aspect of the present disclosure,
there is provided a base station for transmitting information in a
wireless communication system. The base station includes a
transceiver; and a controller coupled with the transceiver and
configured to control to generate information on a channel sensing
operation of a user equipment (UE) in an unlicensed band, wherein
the information on the channel sensing operation indicates one of a
first type performing the channel sensing operation using a
variable time period, a second type performing the channel sensing
operation using a fixed time period, and a third type not
performing the channel sensing operation, and transmit, to the UE,
the information on the channel sensing operation.
[0036] In accordance with another aspect of the present disclosure,
there is provided a method for transmitting information by a base
station in a wireless communication system. The method includes
generating information on a channel sensing operation of a user
equipment (UE) in an unlicensed band, wherein the information on
the channel sensing operation indicates one of a first type
performing the channel sensing operation using a variable time
period, a second type performing the channel sensing operation
using a fixed time period, and a third type not performing the
channel sensing operation; and transmitting, to the UE, the
information on the channel sensing operation.
[0037] In accordance with another aspect of the present disclosure,
there is provided a UE for receiving information in a wireless
communication system. The UE includes a transceiver; and a
controller coupled with the transceiver and configured to control
to receive, from a base station, information on a channel sensing
operation of the UE in an unlicensed band, wherein the information
on the channel sensing operation indicates one of a first type
performing the channel sensing operation using a variable time
period, a second type performing the channel sensing operation
using a fixed time period, and a third type not performing the
channel sensing operation, and transmit an uplink signal based on
the information on the channel sensing operation.
[0038] In accordance with another aspect of the present disclosure,
there is provided a method for receiving information by a UE in a
wireless communication system. The method includes receiving, from
a base station, information on a channel sensing operation of the
UE in an unlicensed band, wherein the information on the channel
sensing operation indicates one of a first type performing the
channel sensing operation using a variable time period, a second
type performing the channel sensing operation using a fixed time
period, and a third type not performing the channel sensing
operation; and transmitting an uplink signal based on the
information on the channel sensing operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The above and other aspects, features, and advantages of
certain embodiments of the present disclosure will be more apparent
from the following detailed description taken in conjunction with
the accompanying drawings, in which:
[0040] FIGS. 1A and 1B are diagrams illustrating a conventional
communication system;
[0041] FIG. 2 is a diagram illustrating a channel occupation
operation based on a channel sensing operation;
[0042] FIG. 3 is a diagram illustrating a channel access scheme for
an unlicensed band of a WiFi system;
[0043] FIG. 4 is a flowchart of a method for a channel access
scheme for an unlicensed band of an LAA system, according to an
embodiment of the present disclosure;
[0044] FIG. 5 is a diagram of a method for performing a channel
sensing operation, according to an embodiment of the present
disclosure;
[0045] FIG. 6 is a diagram of a method for setting a contention
window and a channel sensing period, according to an embodiment of
the present disclosure;
[0046] FIG. 7 is a flowchart of a method for setting a contention
window in a base station for a channel sensing operation, according
to an embodiment of the present disclosure;
[0047] FIG. 8 is a flowchart of a method for setting a contention
window in a terminal for a channel sensing operation, according to
an embodiment of the present disclosure;
[0048] FIG. 9 is a diagram of a base station apparatus, according
to an embodiment of the present disclosure; and
[0049] FIG. 10 is a diagram illustrating of a terminal apparatus,
according to an embodiments of the present disclosure.
DETAILED DESCRIPTION
[0050] Embodiments of the present disclosure will be described
herein below with reference to the accompanying drawings. However,
the embodiments of the present disclosure are not limited to the
specific embodiments and should be construed as including all
modifications, changes, equivalent devices and methods, and/or
alternative embodiments of the present disclosure.
[0051] The terms "have," "may have," "include," and "may include"
as used herein indicate the presence of corresponding features (for
example, elements such as numerical values, functions, operations,
or parts), and do not preclude the presence of additional
features.
[0052] The terms "A or B," "at least one of A or/and B," or "one or
more of A or/and B" as used herein include all possible
combinations of items enumerated with them. For example, "A or B,"
"at least one of A and B," or "at least one of A or B" means (1)
including at least one A, (2) including at least one B, or (3)
including both at least one A and at least one B.
[0053] The terms such as "first" and "second" as used herein may
modify various elements regardless of an order and/or importance of
the corresponding elements, and do not limit the corresponding
elements. These terms may be used for the purpose of distinguishing
one element from another element. For example, a first user device
and a second user device may indicate different user devices
regardless of the order or importance. For example, a first element
may be referred to as a second element without departing from the
scope the present disclosure, and similarly, a second element may
be referred to as a first element.
[0054] It will be understood that, when an element (for example, a
first element) is "(operatively or communicatively) coupled
with/to" or "connected to" another element (for example, a second
element), the element may be directly coupled with/to another
element, and there may be an intervening element (for example, a
third element) between the element and another element. To the
contrary, it will be understood that, when an element (for example,
a first element) is "directly coupled with/to" or "directly
connected to" another element (for example, a second element),
there is no intervening element (for example, a third element)
between the element and another element.
[0055] The expression "configured to (or set to)" as used herein
may be used interchangeably with "suitable for," "having the
capacity to," "designed to," " adapted to," "made to," or "capable
of" according to a context. The term "configured to (set to)" does
not necessarily mean "specifically designed to" in a hardware
level. Instead, the expression "apparatus configured to . . . " may
mean that the apparatus is "capable of . . . " along with other
devices or parts in a certain context. For example, "a processor
configured to (set to) perform A, B, and C" may mean a dedicated
processor (e.g., an embedded processor) for performing a
corresponding operation, or a generic-purpose processor (e.g., a
CPU or an application processor) capable of performing a
corresponding operation by executing one or more software programs
stored in a memory device.
[0056] The term "module" as used herein may be defined as, for
example, a unit including one of hardware, software, and firmware
or two or more combinations thereof. The term "module" may be
interchangeably used with, for example, the terms "unit", "logic",
"logical block", "component", or "circuit", and the like. The
"module" may be a minimum unit of an integrated component or a part
thereof. The "module" may be a minimum unit performing one or more
functions or a part thereof. The "module" may be mechanically or
electronically implemented. For example, the "module" may include
at least one of an application-specific integrated circuit (ASIC)
chip, field-programmable gate arrays (FPGAs), or a
programmable-logic device, which is well known or will be developed
in the future, for performing certain operations.
[0057] The terms used in describing the various embodiments of the
present disclosure are for the purpose of describing particular
embodiments and are not intended to limit the present disclosure.
As used herein, the singular forms are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. All of the terms used herein including technical or
scientific terms have the same meanings as those generally
understood by an ordinary skilled person in the related art unless
they are defined otherwise. The terms defined in a generally used
dictionary should be interpreted as having the same or similar
meanings as the contextual meanings of the relevant technology and
should not be interpreted as having ideal or exaggerated meanings
unless they are clearly defined herein. According to circumstances,
even the terms defined in this disclosure should not be interpreted
as excluding the embodiments of the present disclosure.
[0058] Electronic devices according to the embodiments of the
present disclosure may include at least one of, for example, smart
phones, tablet personal computers (PCs), mobile phones, video
telephones, electronic book readers, desktop PCs, laptop PCs,
netbook computers, workstations, servers, personal digital
assistants (PDAs), portable multimedia players (PMPs), Motion
Picture Experts Group (MPEG-1 or MPEG-2) Audio Layer 3 (MP3)
players, mobile medical devices, cameras, or wearable devices.
According to an embodiment of the present disclosure, the wearable
devices may include at least one of accessory-type wearable devices
(e.g., watches, rings, bracelets, anklets, necklaces, glasses,
contact lenses, or head-mounted-devices (HMDs)), fabric or clothing
integral wearable devices (e.g., electronic clothes), body-mounted
wearable devices (e.g., skin pads or tattoos), or implantable
wearable devices (e.g., implantable circuits).
[0059] The electronic devices may be smart home appliances. The
smart home appliances may include at least one of, for example,
televisions (TVs), digital versatile disk (DVD) players, audios,
refrigerators, air conditioners, cleaners, ovens, microwave ovens,
washing machines, air cleaners, set-top boxes, home automation
control panels, security control panels, TV boxes (e.g., Samsung
HomeSync.TM., Apple TV.TM., or Google TV.TM.), game consoles (e.g.,
Xbox.TM. and PlayStation.TM.), electronic dictionaries, electronic
keys, camcorders, or electronic picture frames.
[0060] The electronic devices may include at least one of various
medical devices (e.g., various portable medical measurement devices
(such as blood glucose meters, heart rate monitors, blood pressure
monitors, or thermometers, and the like), a magnetic resonance
angiography (MRA) device, a magnetic resonance imaging (MRI)
device, a computed tomography (CT) device, scanners, or ultrasonic
devices, and the like), navigation devices, global positioning
system (GPS) receivers, event data recorders (EDRs), flight data
recorders (FDRs), vehicle infotainment devices, electronic
equipment for vessels (e.g., navigation systems, gyrocompasses, and
the like), avionics, security devices, head units for vehicles,
industrial or home robots, automatic teller machines (ATMs), points
of sales (POSs) devices, or Internet of things (IoT) devices (e.g.,
light bulbs, various sensors, electric or gas meters, sprinkler
devices, fire alarms, thermostats, street lamps, toasters, exercise
equipment, hot water tanks, heaters, boilers, and the like).
[0061] The electronic devices may further include at least one of
parts of furniture or buildings/structures, electronic boards,
electronic signature receiving devices, projectors, or various
measuring instruments (such as water meters, electricity meters,
gas meters, or wave meters, and the like). The electronic devices
may be one or more combinations of the above-mentioned devices. The
electronic devices may be flexible electronic devices. Also, the
electronic devices are not limited to the above-mentioned devices,
and may include new electronic devices according to the development
of new technologies.
[0062] Hereinafter, the electronic devices according to various
embodiments of the present disclosure will be described with
reference to the accompanying drawings. The term "user" as used
herein may refer to a person who uses an electronic device or may
refer to a device (e.g., an artificial intelligence electronic
device) which uses an electronic device.
[0063] According to the present disclosure, it is possible to
improve coexistence performance of a channel occupation operation
between devices using an unlicensed band, thereby clearly setting a
standard for the channel occupation operation.
[0064] Although the present disclosure is described herein using an
LTE system and an LTE-A system, the present disclosure may be
applied to other communication systems using a licensed band and an
unlicensed band.
[0065] FIG. 4 is a flowchart of a channel access method for
unlicensed band of an LAA system, according to an embodiment of the
present disclosure.
[0066] A channel occupancy method using an unlicensed band in an
LAA system will be described with reference to FIG. 4. In step 401,
an LAA cell (or LAA SCell, LAA Cell, LAA base station) that does
not require data transmission maintains an idle state. The idle
state is a state in which the LAA cell does not transmit a data
signal to an unlicensed band. For example, the idle is a state in
which an LAA cell, in an active state, has no more data signal to
be transmitted, or has data to be transmitted to the terminal but
does not transmit the data to the terminal.
[0067] When it is required that the LAA cell, in the idle state,
occupies a channel to transmit data or control signal to the
terminal in step 402, the LAA cell may perform a first channel
sensing operation or function in step 403. The first channel
sensing operation may be set to be different depending on at least
one condition of a preset time (e.g., 34 us), a time set by other
device, and a kind of data or control signal to be transmitted in
the LAA cell.
[0068] For example, a time for performing the first channel sensing
operation, in a case in which the LAA cell only transmits the
control signal without data transmitted to a specific terminal, may
be set to be different (e.g., when only transmitting the control
signal, the first channel sensing operation is performed for a time
shorter than that of a case of transmitting a data signal) from a
time for performing the first channel sensing operation, in a case
in which the LAA cell transmits data to the specific terminal.
[0069] Values that may be set for the first channel sensing
operation may be defined in advance. At least one of other
variables (e.g., a threshold value of an intensity of a received
signal for determining whether the channel is occupied) of the
first channel sensing operation in addition to the time for
performing the first channel sensing operation may be set to be
different between the case in which the LAA cell only transmits the
control signal without data transmitted to a specific terminal and
the case in which the LAA cell transmits data to the specific
terminal.
[0070] The LAA cell may set a contention window used in a second
channel sensing operation to an initial value. The first channel
sensing operation is an operation for determining whether other
devices occupy the corresponding channel using various methods
including at least one of a method of measuring intensity of a
received signal and a method of detecting a signal defined in
advance, during the time set for the first channel sensing
operation. The variables required for the first channel sensing
operation including a time for performing the first channel sensing
operation may use a preset value, or may be set by other
devices.
[0071] When it is determined that the channel is in the idle state
in step 404, the LAA cell may occupy the channel and transmit a
signal in step 405. When it is determined that the channel is
occupied by other devices in step 404, a random variable N may be
selected in a contention window [x, y] set in step 407. An initial
contention window may be set in advance (or may be reset) from the
base station. Further, the set contention window may be set using
various values including the number of attempts for occupying the
channel, occupancy rate for the cannel (e.g., traffic load), and a
reception result (e.g., ACK/NACK) of the terminal for the data
signal transmitted at the time of occupying the channel.
[0072] When it is determined that the LAA cell occupying the
channel in step 405 needs to additionally occupy the channel in
step 406, the contention window may be set (reset) in step 414
using a result of data transmission performed in step 405 or at
least one of various methods as mentioned above. The method for
setting the contention window using the result of data transmission
in step 405 is only one example, and the contention window may be
set by a previous channel occupancy and data transmission step or a
preset value.
[0073] When the LAA cell transmits data to the terminal in the
channel occupancy period and receives NACK as a reception result
for the data transmission from the terminal, the LAA cell may
increase or maintain the contention window. When the LAA cell
occupying the channel using the increased or maintained contention
window transmits data to the terminal in the channel occupancy
period and receives ACK as a reception result for the data
transmission from the terminal, the LAA cell may decrease or
maintain the contention window or set the contention window as an
initial contention window. The method for setting a contention
window using the ACK/NACK is merely an example, and the contention
window may be set using other reference values.
[0074] When the random variable N is set in the preset contention
window in step 407, a second channel sensing operation may be
performed using the set N in step 408. The second channel sensing
operation is an operation for determining whether the channel is
occupied using at least one of a method of measuring intensity of
received signal and a method of detecting signal defined in
advance, during a set time, and determination criteria different
from that of the first sensing operation may be set. That is, a
time for performing the second channel sensing operation may be set
to be the same as or shorter than that for performing the first
channel sensing operation. For example, the time for performing the
first channel sensing operation may be set to be 34 us, and the
time for performing the second channel sensing operation may be set
to be 9 us. Further, a reference threshold value of the second
channel sensing operation may be set to be different from a
reference threshold value of the first channel sensing
operation.
[0075] When it is determined that the channel sensed in step 408 is
an idle channel in step 409, 1 is subtracted from the set variable
N in step 410. A different value, however, may be subtracted
depending on a set value, or the subtracted value may be set to be
different depending on a kind or characteristics of signals to be
transmitted by the LAA cell.
[0076] When a subtracted value of the variable N is 0 in step 411,
the LAA cell may perform channel occupancy and data transmission in
step 405. When the value of the variable N is not 0 in step 411,
the LAA cell may perform the second channel sensing operation again
in step 408. When it is determined that the channel is not the idle
channel in step 408 through the second channel sensing operation in
step 409, the LAA cell may perform a third channel sensing
operation through step 412. The third channel sensing operation may
be set identically to the first channel sensing operation or the
second channel sensing operation. For example, both of a time for
performing the first channel sensing operation and a time for
performing the third channel sensing operation may be set to be 34
us. The reference threshold value of the first channel sensing
operation may be set to be different from a reference threshold
value of the third channel sensing operation. The time for
performing the channel sensing operation and the threshold value
are merely examples, and variables or reference values required for
the third channel sensing operation may be set to be the same as
those of the first channel sensing operation or at least one of
them may be set to be different from those of the first channel
sensing operation.
[0077] Further, the third channel sensing operation may be set to
perform an operation generating time delay without a separate
operation for sensing or occupying the channel. The time for
performing the third channel sensing operation may be set to be
identical or different from at least one of those for performing
the first channel sensing operation or the second channel sensing
operation. The LAA cell determines whether other devices occupy the
channel in step 413 using the reference values set for the third
channel sensing operation. When the determined channel occupancy
state is the idle state, the second channel sensing operation may
be performed again in step 408. In a case in which the channel
occupancy state determined in step 413 is not the idle state, the
LAA cell may perform the set third channel sensing operation in
step 412. At least one of the first channel sensing operation, the
second channel sensing operation, and the third channel sensing
operation may be omitted depending on the type or characteristics
of the data or control signal to be transmitted by the LAA
cell.
[0078] When the LAA cell only transmits the control signal (e.g.,
discovery reference signal (DRS)), the LAA cell may immediately
occupy the channel after performing only the first channel sensing
operation according to the result of the channel sensing operation.
The DRS is merely an example in which at least one of the first
channel sensing operation, the second channel sensing operation,
and the third channel sensing operation may be omitted, and the DRS
may also be applied at the time of transmitting other control
signal.
[0079] If the terminal performs an uplink channel occupancy or an
uplink channel sensing operation for uplink transmission by the
above described channel sensing method and the channel occupation
method, each terminal may independently perform the channel sensing
operation. If the terminal independently performs a channel sensing
operation, each terminal has a different channel sensing period
that is randomly selected in the contention window as in step 407.
Therefore, if a plurality of terminals are scheduled in one uplink
subframe, a terminal of which the channel sensing operation ends
first among the terminals may start uplink transmission first.
Therefore, a terminal that is performing the channel sensing
operation may not complete the channel sensing operation due to an
uplink signal transmitted by the terminal. That is, in the above
case, only the terminal of which the channel sensing operation ends
first may perform the set uplink transmission.
[0080] Accordingly, the present disclosure proposes a method in
which a base station sets a channel sensing period based on the
uplink signal reception result received from the terminal, and
performs a setting of the set channel sensing period for terminals
such that the plurality of terminals may perform the channel
sensing operation at the same time, in order for the terminals of
which uplink transmission is set in the same subframe not to set
different channel sensing periods from each other.
[0081] FIG. 5 is a diagram of a method for performing a channel
sensing operation, according to an embodiment of the present
disclosure.
[0082] In view of an LAA cell and an LAA terminal receiving control
and data signals from the LAA cells, an uplink channel sensing
operation and a channel access method of the LAA terminal will be
described with reference to FIG. 5.
[0083] The LAA terminal may receive scheduling information for
uplink transmission in subframe n to subframe n+K from one cell of
cells operating in an unlicensed band or a licensed band. K may be
defined by the base station and the terminal in advance or set by
the base station through a higher layer signal for the terminal, or
the base station may perform a setting of a time relation between
an uplink transmission setting point in time and a start point in
time of the set uplink transmission for the terminal by including
the K value in uplink transmission setting information (for
example, DCI format 0, 4, or DCI format modified for newly
introduced for setting uplink transmission).
[0084] For convenience of explanation, a case in which K=4 (ms)
will be assumed and explained, but K may be set to a value greater
than or equal to than 1 ms. In order to minimize delay between the
uplink transmission setting and actual uplink transmission, K may
also be set in a unit less than K=1 (ms).
[0085] If the set uplink signal transmission is uplink transmission
for an unlicensed band, the terminal performs a channel sensing
operation before performing the set uplink transmission, and if it
is determined that the unlicensed band is in an idle state, the set
uplink transmission may be performed. If it is determined that the
unlicensed band is occupied by other devices, the terminal may not
perform the set uplink transmission.
[0086] When downlink transmission of the LAA cell is performed when
the LAA terminal performs the channel sensing operation for the
unlicensed band, the LAA terminal may determine that the channel is
occupied by other devices due to a downlink signal of the LAA cell.
Accordingly, the LAA cell and the LAA terminal may transmit no
signal in the time and frequency resources immediately before
performing the unlink transmission or when the LAA terminal
performs the channel sensing operation for the unlicensed band.
[0087] The channel sensing operation performed by the LAA terminal
for an unlicensed band may be performed by using at least one of
the following methods:
[0088] Method 1: Uplink signal transmission for a fixed time after
sensing a channel for an unlicensed band;
[0089] Method 2: Uplink signal transmission for a variable time
after sensing a channel for an unlicensed band; and
[0090] Method 3: Uplink signal transmission without sensing a
channel.
[0091] With respect to Method 1, the LAA terminal of which uplink
signal transmission is set in an unlicensed band may perform a
channel sensing operation for the unlicensed band in which the
uplink signal transmission is set for a fixed channel sensing
period 525 before the set uplink signal transmission. If a point in
time when the channel sensing operation ends is earlier than the
set uplink signal transmission point in time, the terminal may
transmit an occupancy signal 550 for occupying the channel from the
point in time when the channel sensing operation ends to the uplink
signal transmission point in time. If the channel sensing operation
ends immediately before the uplink signal transmission point in
time, the occupancy signal may not be transmitted. The occupancy
signal may be one of an implementation signal that may be
differently transmitted depending on implementation of a terminal,
a signal in a preamble form (e.g., PRACH), and an SRS signal.
[0092] Method 1 is a method in which a channel sensing operation
for an unlicensed band in which uplink signal transmission is set
is performed for a fixed channel sensing period at a fixed point in
time. For example, the channel sensing operation may be performed
at a position where the channel sensing operation may end
immediately before starting of a first symbol transmitted in an
uplink subframe in which the uplink signal transmission is set, or
the channel sensing operation may be performed at a starting point
in time of the last OFDM symbol in a subframe immediately before
the uplink subframe in which the uplink signal transmission is set.
The channel occupancy signal may be transmitted immediately before
starting of the first symbol transmitted in the uplink subframe in
which the uplink signal transmission is set. Further, the channel
sensing operation may be performed in the first OFDM or SC-FDMA
symbol in the uplink subframe in which the uplink signal
transmission is set.
[0093] The channel sensing operation may be performed at a position
where the channel sensing operation may end immediately before
starting of a second OFDM or SC-FDMS symbol in the uplink subframe,
or the channel sensing operation may be performed at a starting
point in time of the first OFDM or SC-FDMA symbol in a subframe of
the uplink subframe in which the uplink signal transmission is set.
The channel occupancy signal may be transmitted to immediately
before starting of the second symbol transmitted in the uplink
subframe in which the uplink signal transmission is set.
[0094] With respect to Method 2, the LAA terminal of which uplink
signal transmission is set in an unlicensed band may perform a
channel sensing operation for the unlicensed band in which the
uplink signal transmission is set for a channel sensing period 535
that is set before the set uplink signal transmission. The channel
sensing period 535 may be randomly selected in a contention window
of the LAA terminal or set by the base station. Further, the
channel sensing period 535 may be configured of one fixed period
533 and one or more variable periods 537. The channel sensing
period 535 may also be configured of the variable periods 537
without the fixed period 533, or may also be configured of only one
variable period.
[0095] Further, Method 2 is a method in which a channel sensing
operation for an unlicensed band in which uplink signal
transmission is set is continuously performed at a random point in
time. For example, the channel sensing operation may be performed
at a position where the channel sensing operation may end
immediately before starting of a first symbol transmitted to the
channel sensing period in an uplink subframe in which the uplink
signal transmission is set, or the channel sensing operation may be
performed at a starting point in time of the last OFDM symbol in a
subframe immediately before the uplink subframe in which the uplink
signal transmission is set. At this point, the channel occupancy
signal may be transmitted to immediately before starting of the
first symbol transmitted in the uplink subframe in which the uplink
signal transmission is set.
[0096] Further, the channel sensing operation may be performed in
the first OFDM or SC-FDMA symbol in the uplink subframe in which
the uplink signal transmission is set. Further, the channel sensing
operation may be performed in the first OFDM or SC-FDMA symbol in
the set uplink subframe. The channel sensing operation may be
performed at a position where the channel sensing operation may end
immediately before a starting of a second OFDM or SC-FDMS symbol in
the uplink subframe, or the channel sensing operation may be
performed at a starting point in time of the first OFDM or SC-FDMA
symbol in a subframe of the uplink subframe in which the uplink
signal transmission is set. The channel occupancy signal may be
transmitted to immediately before, starting of the second symbol
transmitted in the uplink subframe in which the uplink signal
transmission is set.
[0097] The base station may inform of or provide a size of a
contention window of the LAA terminal, and the LAA terminal may
randomly set a channel sensing period within the contention window.
Information on the channel sensing period may be informed or
provided to the terminal setting uplink transmission when the base
station transmits uplink control information of the terminal or may
be informed to all terminals through a common downlink control
channel.
[0098] The LAA terminal can have a preset contention window size
and may use (or change) the contention window size in consideration
of a retransmission scheduling related value (e.g., a new data
indicator (NDI)) transmitted from the base station.
[0099] If a point in time when the channel sensing operation ends
is earlier than the set uplink signal transmission point in time,
the terminal may transmit an occupancy signal 550 for occupying the
channel from the point in time when the channel sensing operation
ends to the uplink signal transmission point in time. At this
point, if the channel sensing operation ends immediately before the
uplink signal transmission point in time, the occupancy signal may
not be transmitted. The occupancy signal may be one of an
implementation signal that may be differently transmitted depending
on implementation of a terminal, a signal in a preamble form (e.g.,
PRACH), and an sounding reference signal (SRS) signal.
[0100] With respect to Method 3, the LAA terminal of which uplink
signal transmission is set in an unlicensed band may perform the
set uplink signal transmission without a separate channel sensing
operation before the set uplink signal transmission. Method 3 may
be applied to a case in which after an LAA cell performs a channel
sensing operation for downlink transmission, the LAA cell occupying
the channel sets uplink signal transmission of an LAA terminal
through a downlink control channel, and uplink transmission 510 of
the LAA terminal is performed immediately after downlink
transmission 500 of the LAA cell ends, or ending of the downlink
transmission 500 of the LAA cell and starting of the uplink
transmission 510 of the LAA terminal are performed within a
predetermined time 505 (e.g., within 25 us).
[0101] At least one of the methods for a channel sensing operation
(Method 1, Method 2, or Method 3) and a channel sensing period for
the method may be set to be different depending on whether a cell
setting the uplink signal transmission (or a cell scheduling uplink
transmission) is a licensed band cell or an unlicensed band cell.
If the cell setting the uplink signal transmission is an unlicensed
band cell, at least one of the methods for a channel sensing
operation and a channel sensing period may be set to be different
depending on whether the cell setting the uplink signal
transmission is the same unlicensed band cell as the cell in which
the terminal performs uplink signal transmission, or an unlicensed
band cell that is different from the cell in which the uplink
signal transmission is performed among unlicensed band cells. When
the uplink signal transmission is set in an unlicensed band cell
that is operated in another spectrum that is different from a
licensed band or an unlicensed band cell in which uplink signal
transmission is performed, the uplink channel sensing operation may
be set to be performed according to Method 2, and when the uplink
signal transmission is set in the same unlicensed band cell as the
unlicensed band cell in which uplink signal transmission is
performed, the uplink channel sensing operation may be set to be
performed according to Method 1. When the uplink signal
transmission is set in an unlicensed band cell that is operated in
other spectrum that is different from a licensed band or an
unlicensed band cell in which uplink signal transmission is
performed, a required length of a channel sensing operation period
may be set to be longer than a required length of a channel sensing
operation period when the uplink signal transmission is set in the
same unlicensed band cell as the unlicensed band cell in which
uplink signal transmission is performed. In Method 2, a required
minimum average length of a channel sensing operation period may be
set to be different by differently setting a minimum value or a
maximum value of a contention window depending on a cell in which
the uplink signal transmission is set.
[0102] For example, in Method 1, a size of a channel sensing period
(in a case in which a cell setting uplink signal transmission is a
licensed band cell, or in a case in which a cell setting uplink
signal transmission is an unlicensed band cell that is different
from an unlicensed cell in which uplink signal transmission is
performed among unlicensed band cells) may be set to be greater
than or equal to that in a case in which a cell setting uplink
signal transmission is the same unlicensed band cell as the
unlicensed cell in which uplink signal transmission is performed
among unlicensed band cells. A size of a channel sensing period
that is set to be different depending on a cell setting the uplink
signal transmission may be set by a higher layer signal or defined
in advance. The size of the channel sensing period may be set to be
different depending on a set kind of uplink signal. A size of a
channel sensing period in a case of transmitting an uplink signal
including an uplink data channel may be set to be greater than or
equal to that in a case of transmitting an uplink signal (e.g.,
uplink control channel, SRS, PRACH, etc.) that does not include an
uplink data channel.
[0103] In Method 2, a size of a channel sensing period or a size of
a contention window (in a case in which a cell setting uplink
signal transmission is a licensed band cell, or in a case in which
a cell setting uplink signal transmission is an unlicensed band
cell that is different from an unlicensed cell in which uplink
signal transmission is performed among unlicensed band cells) may
be set to be greater than or equal to those in a case in which a
cell setting uplink signal transmission is the same unlicensed band
cell as the unlicensed cell in which uplink signal transmission is
performed among unlicensed band cells. A size of a channel sensing
period or a size of a contention window that is set to be different
depending on a cell setting the uplink signal transmission may be
set by a higher layer signal or defined in advance. The size of the
channel sensing period or the size of the contention window may be
set to be different depending on a set kind of uplink signal. For
example, a size of a channel sensing period or a size of a
contention window in a case of transmitting an uplink signal
including an uplink data channel may be set to be greater than or
equal to than those in a case of transmitting an uplink signal
(e.g., uplink control channel, SRS, PRACH, etc.) that does not
include an uplink data channel.
[0104] The base station may differently set the uplink channel
sensing operation and at least one of relevant variable values
depending on a kind or characteristics of a cell setting uplink
signal transmission (e.g., when a cell setting uplink signal
transmission is a licensed band cell, when a cell setting uplink
signal transmission is an unlicensed band cell that is different
from an unlicensed cell in which uplink signal transmission is
performed among unlicensed band cells, or when a cell setting
uplink signal transmission is the same unlicensed band cell as the
unlicensed cell in which uplink signal transmission is performed
among unlicensed band cells), or depending on a kind or
characteristics of an uplink transmission signal of the terminal
(e.g., in a case of transmitting an uplink signal including an
uplink data signal, or in a case of transmitting an uplink control
signal or control channel without including an uplink data signal),
and may perform a setting of the set channel sensing operation and
variable values for the terminal using a higher layer signal. For
example, in a case in which a cell setting uplink signal
transmission is a licensed band cell, or in a case in which a cell
setting uplink signal transmission is an unlicensed band cell that
is different from an unlicensed cell in which uplink signal
transmission is performed among unlicensed band cells, a channel
sensing operation using a variable period like Method 2 may be set
or defined in advance, and in a case in which a cell setting uplink
signal transmission is the same unlicensed band cell as the
unlicensed cell in which uplink signal transmission is performed
among unlicensed band cells, a channel sensing operation using a
fixed period like Method 1 may be set or defined in advance.
[0105] The base station may perform a setting of a method for a
channel sensing operation for the terminal by including a field for
setting a method (LBT type) for a channel sensing operation to be
performed by the terminal in uplink transmission setting
information of the terminal.
[0106] The base station may transmit the information on the channel
sensing type to the UE through a UL grant. The information on the
channel sensing type may be information for setting whether to
perform the channel sensing operation using the fixed time period
like the Method 1 or whether to perform the channel sensing
operation using the variable time period like the Method 2.
[0107] Based on the information on the channel sensing type, the UE
may transmit the uplink signal to the base station after performing
the channel sensing operation during the fixed time period
according to the Method 1. In addition, based on the information on
the channel sensing type, the UE may transmit the uplink signal to
the base station after performing the channel sensing operation
during the variable time period according to the Method 2. The
variable time period may be randomly set based on the contention
window for the UE. For example, the variable time period may be
determined based on a randomly selected value and a minimum sensing
slot in the contention window.
[0108] The terminal receiving the uplink transmission setting
information may perform a channel sensing operation for the set
uplink unlicensed band according to the method for a channel
sensing operation (or LBT type) included in the information and
instructed by the base station. Detailed information (e.g., a
length of a channel sensing period, a size of a contention window,
etc.) required for the channel sensing operation may be defined in
advance by the base station and the terminal, set by base station
for the terminal through a higher layer signal, or set for the
terminal by being included in the uplink transmission setting
information.
[0109] When the base station sets uplink transmission of the
terminal, in a case in which information (e.g., a length of a
channel sensing period, or a size of a contention window) required
for a channel sensing operation of the terminal is set for the
terminal, if one or more terminals are scheduled in a subframe in
which the corresponding uplink transmission is set, e.g., an uplink
subframe n, the base station may inform terminals of a length of a
channel sensing period or a size of a contention window that is
determined for each terminal through the channel sensing operation,
respectively, as the information required by one or more terminals
of which uplink transmission is set in the subframe n for a channel
sensing operation (a length of a channel sensing period or a size
of a contention window). When the terminal performing the channel
sensing operation in the subframe n, however, uses different
lengths of a channel sensing period, or different sizes of a
contention window to perform the channel sensing operation, if
there is a terminal that ends first the channel sensing operation,
and occupies the channel to perform uplink transmission among the
terminals, other terminals receiving an uplink signal transmitted
by the terminal may not properly perform a channel sensing
operation. Accordingly, the base station may inform each terminal
of the same length of a channel sensing period or the same size of
a contention window as the information (a length of a channel
sensing period, or a size of a contention window) required by the
one or more terminals of which uplink transmission is set in the
subframe n for a channel sensing operation, respectively. In
determining the same length of a channel sensing period or the same
size of a contention window, the base station may select a maximum
value of lengths of a channel sensing period or sizes of a
contention window that are determined for each terminal of which
uplink transmission is set in the subframe n, and the base station
may inform the terminals performing uplink transmission in the
subframe n of the maximum value. As another method, the base
station may also perform a setting so that the terminals having the
same value among lengths of a channel sensing period or sizes of a
contention window that are determined for respective terminals of
which uplink transmission is set in the subframe n perform uplink
transmission in the subframe n.
[0110] Further, the base station selects a value to be used in the
subframe n among lengths of a channel sensing period or sizes of a
contention window that are determined for respective terminals of
which uplink transmission is set in the subframe n. The base
station also calculates a position and the number of symbols
excluded from uplink transmission in the uplink subframe n, or a
position of a start symbol and a position of an end symbol in which
uplink transmission is actually performed in the uplink subframe n,
based on the selected length of a channel sensing period or the
selected size of a contention window. Even in a case in which the
base station differently informs respective terminals of a length
of a channel sensing period or a size of a contention window, at
least one of a position of a start symbol and a position of an end
symbol in which uplink transmission is actually performed in the
uplink subframe n needs to be identically set for the terminals
performing uplink transmission in the uplink subframe n. If an
uplink transmission starting point in time of one or more terminals
is different in the uplink subframe n, other terminals receiving an
uplink signal transmitted by the terminal may not properly perform
a channel sensing operation.
[0111] Accordingly, the base station may calculate a time required
for an uplink channel sensing operation in the subframe n based on
at least one of a length of a channel sensing period or a size of a
contention window that is determined for each terminal of which
uplink transmission is set in the subframe n, e.g., based on at
least one of a maximum size of a contention window, an average
length of a channel sensing period that may be selected from the
maximum size of a contention window, a maximum average size of a
contention window, and an average length of a channel sensing
period that may be selected from the maximum average size of a
contention window of terminals intending to setting uplink
transmission in the subframe n. The base station may also
identically inform the terminals performing uplink transmission of
an uplink transmission start symbol or an uplink transmission
starting point in time, and an uplink transmission end symbol or an
uplink transmission ending point in time in the subframe n based
thereon.
[0112] The base station may select terminals having at least one
same value of a maximum size of a contention window, an average
length of a channel sensing period that may be selected from the
maximum size of a contention window, a maximum average size of a
contention window, and an average length of a channel sensing
period that may be selected from the maximum average size of a
contention window as the terminals setting uplink transmission in
the subframe n to calculate a time required for an uplink channel
sensing operation in the subframe n. The base station may also
inform the terminals performing uplink transmission of an uplink
transmission start symbol or an uplink transmission starting point
in time, and an uplink transmission end symbol or an uplink
transmission ending point in time in the subframe n based
thereon.
[0113] Further, the terminal can be configured so that uplink
signal transmission in N uplink subframes (multi-subframe
scheduling) may be performed as one uplink transmission setting
information that is transmitted from the base station in a subframe
n for the uplink signal transmission of the terminal in a downlink
control channel of at least one of a licensed band cell, an
unlicensed band cell different from the uplink transmission cell,
and the same unlicensed band cell as the uplink transmission cell
that includes a subframe n+K. A method for a channel sensing
operation that is performed before transmission in one set subframe
or a plurality of set uplink subframes (or UL burst) starts and a
method for a channel sensing operation that is performed by the
terminal occupying the uplink channel in the occupied uplink
subframe may be different from each other. For example, in a
terminal configured so that uplink signal transmission in N uplink
subframes (multi-subframe scheduling) may be performed as one
uplink transmission setting information that is transmitted from
the base station in a subframe n for the uplink signal transmission
of the terminal that includes a subframe n+K, the channel sensing
operation performed before the set uplink subframe (or UL burst)
transmission starts may be performed according to a channel sensing
method having a variable period link Method 2. The channel sensing
operation performed by the terminal occupying an uplink channel by
performing the channel sensing operation according to Method 2 in
the plurality of set uplink subframes may be performed according to
a channel sensing method having a fixed channel sensing period like
Method 1. A required minimum average length of a channel sensing
period of a channel sensing operation (Method 1) performed in the
plurality of set uplink subframes may be set to be shorter than
that of a channel sensing operation (Method 2) performed before the
set uplink subframe (or UL burst) transmission starts.
[0114] Further, in the terminal configured so that uplink signal
transmission in N uplink subframes (multi-subframe scheduling) may
be performed as one uplink transmission setting information that is
transmitted from the base station in a subframe n for the uplink
signal transmission of the terminal in a downlink control channel
of at least one of a licensed band cell, an unlicensed band cell
different from the uplink transmission cell, and the same
unlicensed band cell as the uplink transmission cell includes a
subframe n+K. A method for a channel sensing operation that is
performed before transmission in one set subframe or a plurality of
set uplink subframes (or UL burst) starts and a method for a
channel sensing operation that is performed by the terminal
occupying the uplink channel in the occupied uplink subframe may be
identical to each other. For example, when a terminal 1 configured
so that uplink signal transmission in N uplink subframes
(multi-subframe scheduling) may be performed as one uplink
transmission setting information that is transmitted from the base
station in a subframe n for the uplink signal transmission of the
terminal includes a subframe n+K as described above, and a terminal
2 configured so that uplink signal transmission in some uplink
subframes (M<N) among the N uplink subframes may be performed
coexist, since a channel sensing operation of the terminal 2 exists
in an uplink subframe transmission period of the terminal 1, the
terminal 2 may be configured to perform the same channel sensing
operation as the channel sensing operation performed by the
terminal 1 in the plurality of set uplink subframe. In other words,
in the terminal configured so that uplink signal transmission in N
uplink subframes (multi-subframe scheduling) may be performed as
one uplink transmission setting information that is transmitted
from the base station in a subframe n for the uplink signal
transmission of the terminal in a downlink control channel of at
least one of a licensed band cell, an unlicensed band cell
different from the uplink transmission cell, and the same
unlicensed band cell as the uplink transmission cell includes a
subframe n+K, a channel sensing operation is performed for starting
the set uplink transmission according to a method (LBT type) for a
channel sensing operation included in the uplink transmission
setting. In the N uplink subframe transmission periods, a method
for a channel sensing operation that is the same as the method for
a channel sensing operation included in the uplink transmission
setting may be performed, or a method for a channel sensing
operation that is different from the method for a channel sensing
operation included in the uplink transmission setting may be
performed. When a method for a channel sensing operation that is
different from the method for a channel sensing operation included
in the uplink transmission setting is performed, the method for a
channel sensing operation performed in the N uplink subframe
transmission periods may be defined in advance by the base station
and the terminal, set by the base station for the terminal through
a higher layer signal, or set by the base station for the terminal
by adding a field for setting the method for a channel sensing
operation to the uplink transmission setting information.
[0115] Operations for Method 2 will now be described.
[0116] The base station may set a channel sensing period for uplink
signal transmission of the terminal through a downlink control
channel for the terminal. The channel sensing period may be
configured of a fixed period and/or a variable period, and the
variable period may be randomly selected in an uplink contention
window of the base station. Accordingly, the channel sensing period
may vary depending on a length of a randomly selected variable
period (in other words, the number of the back-off counter).
Therefore, the channel sensing period set by the base station for
the terminal can be a length of the variable period or the number
of the back-off counter. A total channel sensing period required by
the terminal for an uplink channel sensing operation includes a
fixed period and a variable period set by the base station.
[0117] As described above, in order to set a channel sensing period
required for an uplink channel sensing operation of the terminal,
the base station needs to set a contention window. A method for
setting, by the base station, a contention window for an uplink
channel sensing operation can include the base station determining
a reference subframe before a channel sensing period setting point
in time for a channel sensing operation according to a result of
uplink data channel reception of the terminal that is received
before the base station sets a channel sensing period required for
uplink channel sensing operation for the terminal. The base station
can also set a contention window according to an uplink data
channel reception result transmitted from the terminal in the
reference subframe.
[0118] FIG. 6 is a diagram illustrating a method for setting the
contention window and a channel sensing period, according to an
embodiment of the present disclosure.
[0119] Method 2-1: The base station defines a first uplink subframe
620 in a latest uplink transmission period 638 that is set before a
channel sensing period setting point in time 680 for an uplink
channel sensing operation 650 of the terminal as a reference
subframe. The base station increases a contention window when Z% or
more of NACK of the uplink data channel reception result 660
transmitted from the terminal in the reference subframe is
generated.
[0120] Method 2-2: The base station increases a contention window
when Z% or more of NACK of the uplink data channel reception
results 660 and 662 (which is received from the terminal determined
before the channel sensing period setting point in time 680 for the
uplink channel sensing operation 650 of the terminal in the latest
uplink transmission period 638 that is set before the channel
sensing period setting point in time 680 for the uplink channel
sensing operation 650) is generated.
[0121] Method 2-3: The base station increases a contention window
when Z% or more of NACK of the uplink data channel reception result
662 (which is in an uplink subframe that is most recently
determined before the channel sensing period setting point in time
680 for the uplink channel sensing operation 650 of the terminal)
is generated.
[0122] If Z% or more of NACK of the uplink data channel reception
result, which is transmitted from the terminal in the reference
subframe used for changing a contention window in Methods 2-1, 2-2,
and 2-3 is not generated, it is possible to decrease or initialize
the contention window. Z may be defined in advance by the base
station and the terminal, or set by the base station for the
terminal through a higher layer signal as a value of 10, 20, 50,
80, or 100%. The Z value may be defined to be different according
to a regulation for each region or each frequency spectrum.
Further, the Z value may be set to be different depending on
whether a cell setting uplink signal transmission (or a cell
scheduling uplink transmission) is a licensed band cell or an
unlicensed band cell. In other words, if the cell setting the
uplink signal transmission is an unlicensed band cell, the Z value
may be set to be different depending on whether the cell setting
the uplink signal transmission is the same unlicensed band cell as
the cell in which the terminal performs uplink signal transmission,
or an unlicensed band cell that is different from the cell in which
the uplink signal transmission is performed among unlicensed band
cells. For example, when the uplink signal transmission is set in
an unlicensed band cell that is operated in another spectrum that
is different from a licensed band or an unlicensed band cell in
which uplink signal transmission is performed, Z% is set to be low
as compared to a case in which the uplink signal transmission is
set in the same unlicensed band cell as the unlicensed band cell in
which uplink signal transmission is performed, thereby making it
possible to differently set a probability with which a contention
window is changed, depending on whether a channel sensing operation
for the unlicensed band is performed.
[0123] Further, a contention window may be increased by at least
one of an exponential increase method, a linear increase method,
and a method of increasing within a contention window set that is
defined in advance. Moreover, an uplink data channel transmission
result used once for setting a contention window as a reference
subframe may not be used for setting other contention windows.
Additionally, although the base station configures uplink
transmission for an unlicensed band through a licensed band
downlink, in a case in which it is determined that uplink
transmission received from the terminal configuring the uplink
transmission is determined as DTX, if the uplink transmission
determined as DTS as described above is included in a reference
subframe, the uplink transmission result may not be reflected in
criteria for changing a contention window. Although the base
station configures uplink transmission for an unlicensed band
through unlicensed band downlink, in a case in which it is
determined that uplink transmission received from the terminal
configuring the uplink transmission is determined as DTX, if the
uplink transmission determined as DTS as described above is
included in a reference subframe, the uplink transmission result
may be determined as NACK and included in criteria for changing a
contention window. If the base station determines that the uplink
transmission result of the terminal is NACK/DTX, any state, etc.,
the uplink transmission result may be determined as NACK and
included in criteria for changing a contention window.
[0124] A reference subframe that is actually applied in changing a
contention window in Methods 2-1, 2-2, and 2-3 may be different
depending on a point in time when uplink data channel reception
result transmitted from the terminal in the reference subframe is
determined. In other words, a point in time when uplink data
channel reception result transmitted from the terminal in the
reference subframe is determined as ACK/NACK may be different for
each base station.
[0125] For example, in FIG. 6, the base station 1 may determine in
a subframe n+6 an uplink data channel reception result transmitted
from the terminal in a subframe n+4, and another base station 2 may
determine in a subframe n+7 an uplink data channel reception result
transmitted from the terminal in the subframe n+4. To solve the
above problem, the reference subframe may be defined as a reference
subframe that is valid after a predetermined time base on a point
in time when the terminal transmits an uplink data channel. For
example, an uplink data channel reception result transmitted from
the terminal in the subframe n+4 may be determined as valid after a
subframe n+K (e.g., K=3 or 4), and a contention window may be
increased by using one of Methods 2-1, 2-2, and 2-3 when N% or more
of NACK of the uplink data channel reception result transmitted
from the terminal in the valid reference subframe is generated. If
it is assumed that K=3 (even when the base station determines at
666 in a subframe n+9 a transmission result of an uplink data
channel 626 transmitted by the terminal in a subframe n+7) the base
station may not include the transmission result of the uplink data
channel 626 transmitted in the subframe n+7 that does not satisfy
the condition that K=3 in a reference subframe at a channel sensing
period setting point in time n+10 for an uplink channel sensing
operation 650 of the terminal, in Method 2-2. The reference
subframe in Method 2-2 is uplink subframes 620, 622, and 624. As
another example, if it is assumed that K=3 (even when the base
station determines at 666 in a subframe n+9 a transmission result
of an uplink data channel 626 transmitted by the terminal in a
subframe n+7) the base station determines the latest uplink
subframe 624 satisfying the condition that K=3 as a reference
subframe for an uplink channel sensing operation 650 of the
terminal, in Method 2-3.
[0126] The base station may set a size of a contention window for
determining an uplink channel sensing period by at least one of
Methods 2-1, 2-2, and 2-3. The base station may use a plurality of
contention windows corresponding to respective terminals for each
terminal, or may use one contention window capable of being applied
to all terminals. The base station may use a plurality of
contention windows depending on a quality of service (QoS) or LBT
class, or may apply a contention window set to be different for
each QoS or LBT class to all terminals.
[0127] When the base station uses one contention window capable of
being applied to all terminals (or cell-specific contention
window), the base station may set a size of a contention window for
an uplink channel sensing operation according to the determination
result by at least one of Methods 2-1, 2-2, and 2-3. When the base
station uses a plurality of contention windows depending on a QoS
or LBT class (or cell-specific contention window per LBT class),
the base station may set a plurality of contention windows together
according to the determination result by at least one of Methods
2-1, 2-2, and 2-3. For example, when it is determined by the base
station using a contention window 1 for LBT class 1 and a
contention window 2 for LBT class 2 that the contention window
needs to be changed by at least one of Methods 2-1, 2-2, and 2-3,
both the contention window and the contention window 2 may be
increased or initialized together. In a case in which the base
station uses a plurality of contention windows depending on LBT
class, the base station may select an LBT class corresponding to
the uplink transmission period, select a random variable (or
backoff counter) within a contention window for the selected LBT
class, and set the selected variable as the selected channel
sensing period value (or selected variable value) for the terminal
requiring an uplink channel sensing operation.
[0128] The randomly selected channel sensing period value may be
commonly applied to all cases requiring an uplink channel sensing
operation in the uplink transmission period. For example, in order
to perform a channel sensing operation for an LBT class in the
uplink transmission period 658 in FIG. 6, the base station may
select a random variable within a contention window for the
selected LBT class, and set the selected channel sensing period
value for the terminal configuring uplink transmission in a period
658 so that the selected channel sensing period value is commonly
used for uplink channel sensing operations 650, 652, 654, and 656.
In other words, the base station may set one channel sensing period
value for one uplink transmission period, and use the set channel
sensing period value for all uplink channel sensing operations
within the uplink transmission period. The base station may set and
use a channel sensing period value for each uplink channel sensing
operations within the uplink transmission period. The channel
sensing period may be selected within a contention window for the
selected LBT class. In other words, different channel sensing
period values may be selected within one contention period and
applied to uplink channel sensing periods 650, 652, 654, and
656.
[0129] When the base station uses a plurality of contention windows
corresponding to respective terminals for each terminal (or
UE-specific contention window), the base station may set contention
windows of terminals performing uplink signal transmission in an
uplink transmission period 638 in FIG. 6 including a reference
subframe of Method 2-1, 2-2, or 2-3 according to an uplink
transmission result of the terminal determined by at least one of
Methods 2-1, 2-2, and 2-3. In other words, contention windows of
terminals that did not perform uplink signal transmission in the
uplink transmission period 638 including a reference subframe of
Method 2-1, 2-2, or 2-3 maintains previously set contention windows
without being changed. The base station may also set contention
windows of all terminals regardless of whether the uplink signal
transmission is performed in an uplink transmission period 638
including a reference subframe of Method 2-1, 2-2, or 2-3 according
to a result determined by at least one of Methods 2-1, 2-2, and
2-3.
[0130] In the case in which the base station uses a plurality of
contention windows corresponding to respective terminals for each
terminal, a channel sensing period required for an uplink channel
sensing operation may be set by using contention windows of the
terminals that are set so that the uplink channel sensing
operations are performed at the same point in time.
[0131] Referring again to FIG. 6, for example, the base station may
select a random variable (or backoff counter) based on a largest
contention window of contention windows of terminals configuring
uplink transmission 640 in a subframe n+14, and set a channel
sensing period value (or selected variable value) required for the
uplink channel sensing operation 650 for the terminals configuring
the uplink transmission 640 in the subframe n+14 using the selected
variable. Alternatively, the base station may select a random
variable (or backoff counter) within respective contention windows
of terminals configuring uplink transmission 640 in a subframe
n+14, and may select a largest channel sensing period or backoff
counter of the selected variables as a channel sensing period value
required for the uplink channel sensing operation 650 to set the
channel sensing period value required for the uplink channel
sensing operation 650 for the terminals configuring the uplink
transmission 640 in the subframe n+14.
[0132] The base station may set the selected channel sensing period
for the terminal through a downlink control channel. The selected
channel sensing period value (or backoff counter) may be set for
the terminal by being included in control information (DCI) for the
uplink data channel or uplink control signal transmission
configuration of the terminal. A field corresponding to a channel
sensing period value may be set to DCI format 0, 4 or a new DCI
format in addition to variables associated with uplink transmission
and transmitted to the terminal requiring uplink transmission
setting. At this point, the selected channel sensing period value
may also be transmitted to all terminal by using a common search
space of a downlink control channel.
[0133] Unlike Method 2, the base station transmits a result of
uplink signal transmission of the terminal for each terminal, the
terminal sets a contention window based on the uplink signal
transmission result, and a channel sensing period for a channel
sensing operation for uplink transmission set using the set
contention window may be set. In other words, when it is set in
uplink signal setting information of the terminal transmitted by
the base station through a downlink control channel that a base
station reception result for previous uplink signal transmission is
NACK, the terminal may increase the contention window. When it is
set in uplink signal setting information of the terminal
transmitted by the base station through a downlink control channel
that a base station reception result for previous uplink signal
transmission is ACK, the terminal may initialize the contention
window.
[0134] When it is determined that a base station reception result
for previous uplink transmission is NACK regardless of hybrid
automatic repeat request (HARQ) process for the uplink
transmission, the terminal may increase the contention window and
select a channel sensing period value within the increased
contention window. The terminal may divide and use the contention
window for each HARQ process for the uplink transmission. If the
set uplink transmission is set as an HARQ process that is different
from an HARQ process for previous uplink transmission, the terminal
may select a channel sensing period using a contention window
corresponding to the set HARQ process regardless of the base
station reception result for the previous uplink transmission. When
a base station reception result for previous uplink transmission is
NACK, a contention window for the previous uplink transmission is
increased. In a case in which the terminal divides and uses a
contention window for each uplink HARQ process, the terminal may
also select a channel sensing period value based on a largest
contention window of contention windows of the set HARQ
process.
[0135] FIG. 7 is a flowchart of a method for setting a contention
window in a base station for a channel sensing operation, according
to an embodiment of the present disclosure.
[0136] In step 701, contention window setting criteria is set. The
entire uplink transmission period of the terminal or a part of the
uplink transmission period of the terminal among uplink
transmission periods before setting a channel sensing period for an
uplink channel sensing operation may be set as a reference subframe
for setting a contention window. The base station may use a
reception result of uplink transmission of the terminal in the
reference subframe that is determined before setting the channel
sensing period for the uplink channel sensing operation.
[0137] In step 702, a contention window setting reference terminal
is set. A terminal performing transmission in the entire or some
subframes of the uplink transmission period may be set as a
reference terminal.
[0138] In step 703, a contention window changing method is set.
That is, the contention window may be changed using a ratio of NACK
of an uplink signal reception result determined according to the
steps 701 and 702.
[0139] In step 704, the base station receives an uplink signal from
the terminal. In step 705, a reception result of the uplink signal
of the terminal received in step 704 is determined. In step 706, a
contention window is set by determining the uplink reception result
of the terminal that is determined in step 705 based on the
contention window changing criteria set in steps 701, 702 and
703.
[0140] If it is determined in step 706 that the contention window
needs to be increased, the base station increases the contention
window, sets a channel sensing period for an uplink channel sensing
operation within the increased contention window, and sets the
selected channel sensing period for the terminal by including the
channel sensing period in uplink transmission setting information
in step 707. If it is determined in step 706 that the contention
window does not need to be increased, the base station initializes
the contention window, sets a channel sensing period for an uplink
channel sensing operation within the initialized contention window,
and sets the selected channel sensing period for the terminal by
including the channel sensing period in uplink transmission setting
information in step 708.
[0141] FIG. 8 is a flowchart of a method for setting a contention
window in a UE for a channel sensing operation, according to an
embodiment of the present disclosure.
[0142] In step 801, the terminal receives configuration information
for uplink signal transmission from the base station. A channel
sensing period may be included in the uplink signal transmission
setting information. The terminal receiving the channel sensing
period from the base station in step 802 senses a channel during
the channel sensing period before uplink signal transmission set in
step 803.
[0143] If it is determined in step 804 that the channel sensed in
step 803 is in an idle state, the terminal performs the set uplink
signal transmission in step 805. If it is determined in step 804
that the channel sensed in step 803 is being occupied by other
devices, the terminal does not perform the uplink signal
transmission in step 806.
[0144] FIG. 9 is a diagram illustrating a base station apparatus
for setting a contention window and a channel sensing period of the
terminal by the base station using an unlicensed band, according to
an embodiment of the present disclosure.
[0145] A receiver 920 of the base station may perform an operation
for sensing an unlicensed band channel using a set value for a
channel sensing operation set through a controller 900 of the base
station, as well as a function of receiving a signal from the base
station or the terminal, or measuring a channel from the base
station or the terminal. Further, the controller 900 of the base
station may determine a reception result of the signal received
from the terminal through the receiver 920 of the base station, set
a contention window required for a channel sensing operation of the
terminal according to the determination result, and set a channel
sensing period value of the terminal by selecting a random variable
within the set contention window. Further, the controller 900 of
the base station may transmit a control signal configuring uplink
signal transmission of the terminal through a downlink control
channel by including the set channel sensing period value of the
terminal in a transmitter 910 of the base station.
[0146] FIG. 10 is a diagram illustrating a terminal apparatus using
an unlicensed band, according to an embodiment of the present
disclosure.
[0147] A controller 100 of the terminal in FIG. 10 may set a
channel sensing operation so that the terminal performs the channel
sensing operation during a channel sensing period required for
uplink signal transmission in an unlicensed band that is set by the
base station using a receiver 1020. Further, the controller 1000
may configure uplink transmission in time and frequency resources
set according to uplink signal transmission set by the base station
and received through the receiver 1020.
[0148] The receiver 1020 senses a channel during the channel
sensing period set by the controller 1000, and when it is
determined by the controller 1000 that the channel is in an idle
state based on intensity of a signal received by the receiver
during the channel sensing period, a transmitter 1010 may configure
uplink transmission in time and frequency resources set according
to the uplink signal transmission set by the base station.
[0149] While the present disclosure has been shown and described
with reference to certain embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the scope of
the present disclosure. Therefore, the scope of the present
disclosure should not be defined as being limited to the
embodiments, but should be defined by the appended claims and
equivalents thereof.
* * * * *