U.S. patent application number 16/325139 was filed with the patent office on 2019-06-13 for lbt parameters for uplink in unlicensed spectrum.
The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Sorour Falahati, Havish Koorapaty.
Application Number | 20190182865 16/325139 |
Document ID | / |
Family ID | 59895336 |
Filed Date | 2019-06-13 |
![](/patent/app/20190182865/US20190182865A1-20190613-D00000.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00001.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00002.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00003.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00004.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00005.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00006.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00007.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00008.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00009.png)
![](/patent/app/20190182865/US20190182865A1-20190613-D00010.png)
View All Diagrams
United States Patent
Application |
20190182865 |
Kind Code |
A1 |
Falahati; Sorour ; et
al. |
June 13, 2019 |
LBT PARAMETERS FOR UPLINK IN UNLICENSED SPECTRUM
Abstract
According to some embodiments, a method for use in a user
equipment (UE) of managing a listen-before-talk (LBT) contention
window size comprises transmitting a first burst of uplink
subframes after a first LBT procedure performed using an LBT
contention window size, and determining a reference subframe based
on the first burst. The reference subframe is associated with a
reference hybrid automatic repeat request (HARQ) process
identifier. The method further comprises receiving scheduling for a
second burst of uplink subframes. The scheduling comprises an
associated HARQ process identifier and an associated new data
indicator (NDI) for each subframe. When the UE determines the HARQ
process identifier associated with at least one of the subframes of
the second burst matches the reference HARQ process identifier,
then if the associated NDI indicates new data, the method resets
the LBT contention window size, else the method increments the LBT
contention window size.
Inventors: |
Falahati; Sorour;
(STOCKHOLM, SE) ; Koorapaty; Havish; (SARATOGA,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Family ID: |
59895336 |
Appl. No.: |
16/325139 |
Filed: |
August 11, 2017 |
PCT Filed: |
August 11, 2017 |
PCT NO: |
PCT/IB2017/054931 |
371 Date: |
February 12, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62374697 |
Aug 12, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 1/1812 20130101;
H04L 1/1822 20130101; H04W 74/0808 20130101; H04W 74/085 20130101;
H04W 74/004 20130101; H04W 72/0446 20130101; H04L 1/1887
20130101 |
International
Class: |
H04W 74/08 20060101
H04W074/08; H04W 74/00 20060101 H04W074/00; H04W 72/04 20060101
H04W072/04; H04L 1/18 20060101 H04L001/18 |
Claims
1. A method for use in a user equipment (UE) of managing a
listen-before-talk (LBT) contention window size, the method
comprising: transmitting a first burst of uplink subframes after a
first LBT procedure, the LBT procedure performed using an LBT
contention window size; determining a reference subframe based on
the first burst of uplink subframes, the reference subframe
associated with a reference hybrid automatic repeat request (HARQ)
process identifier; receiving scheduling for a second burst of
uplink subframes, the scheduling comprising, for each subframe of
the second burst of uplink subframes, an associated HARQ process
identifier and an associated new data indicator (NDI); when the UE
determines the HARQ process identifier associated with at least one
of the subframes of the second burst of uplink subframes matches
the reference HARQ process identifier and the associated NDI
indicates new data, resetting the LBT contention window size to a
minimum value; when the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates a retransmission, incrementing the
LBT contention window size; and performing a second LBT procedure
using the contention window size.
2. The method of claim 1, wherein determining the reference
subframe comprises determining a most recently transmitted uplink
subframe in the first burst of uplink subframes for which the
associated HARQ process identifier is also found in the received
scheduling for the second burst of uplink subframes.
3. The method of claim 1, wherein determining the reference
subframe comprises determining the first transmitted subframe of
the first burst of uplink subframes for which the HARQ process
identifier associated with the first subframe of the first burst of
uplink subframes is also found in the received scheduling for the
second burst of uplink subframes.
4. The method of claim 1, wherein transmission of the first burst
ended more than a threshold time prior to determining the reference
subframe.
5. The method of claim 4, wherein the threshold time is 4 ms.
6. The method of claim 1, wherein resetting the LBT contention
window size to a minimum value comprises resetting the LBT
contention window size to a minimum value of a set of values
associated with a priority class used by the UE to perform the
first LBT procedure.
7. The method of claim 1, wherein resetting the LBT contention
window size to a minimum value comprises resetting LBT contention
window sizes associated with all priority classes used by the
UE.
8. The method of claim 1, wherein incrementing the LBT contention
window size comprises incrementing the LBT contention window size
to a next value in a set of values associated with a priority class
used by the UE to perform the first LBT procedure.
9. The method of claim 1, wherein incrementing the LBT contention
window size comprises incrementing LBT contention window sizes
associated with all priority classes used by the UE.
10. The method of claim 1, wherein the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is incremented when the NDI associated with
each HARQ process identifier of the plurality of HARQ identifiers
indicates a retransmission.
11. The method of claim 1, wherein the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is reset when at least one NDI associated
with a HARQ process identifier of the plurality of HARQ identifiers
indicates new data.
12. The method of claim 1, wherein performing the second LBT
procedure comprises performing a Category 4 LBT for physical uplink
shared channel (PUSCH) transmission on a licensed assisted access
(LAA) secondary cell.
13. A user equipment (UE) capable of managing a listen-before-talk
(LBT) contention window size, the UE comprising processing
circuitry operable to: transmit a first burst of uplink subframes
after a first LBT procedure, the LBT procedure performed using an
LBT contention window size; determine a reference subframe based on
the first burst of uplink subframes, the reference subframe
associated with a reference hybrid automatic repeat request (HARQ)
process identifier; receive scheduling for a second burst of uplink
subframes, the scheduling comprising, for each subframe of the
second burst of uplink subframes, an associated HARQ process
identifier and an associated new data indicator (NDI); when the UE
determines the HARQ process identifier associated with at least one
of the subframes of the second burst of uplink subframes matches
the reference HARQ process identifier and the associated NDI
indicates new data, reset the LBT contention window size to a
minimum value; when the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates a retransmission, increment the
LBT contention window size; and perform a second LBT procedure
using the contention window size.
14. The UE of claim 13, wherein the processing circuitry is
operable to determine the reference subframe by determining a most
recently transmitted uplink subframe in the first burst of uplink
subframes for which the associated HARQ process identifier is also
found in the received scheduling for the second burst of uplink
subframes.
15. The UE of claim 13, wherein the processing circuitry is
operable to determine the reference subframe by determining the
first transmitted subframe of the first burst of uplink subframes
for which the HARQ process identifier associated with the first
subframe of the first burst of uplink subframes is also found in
the received scheduling for the second burst of uplink
subframes.
16. The UE of claim 14, wherein transmission of the first burst
ended more than a threshold time prior to determining the reference
subframe.
17. The UE of claim 16, wherein the threshold time is 4 ms.
18. The UE of claim 13, wherein the processing circuitry is
operable to reset the LBT contention window size to a minimum value
by resetting the LBT contention window size to a minimum value of a
set of values associated with a priority class used by the UE to
perform the first LBT procedure.
19. The UE of claim 13, wherein the processing circuitry is
operable to reset the LBT contention window size to a minimum value
by resetting LBT contention window sizes associated with all
priority classes used by the UE.
20. The UE of claim 13, wherein the processing circuitry is
operable to increment the LBT contention window size by
incrementing the LBT contention window size to a next value in a
set of values associated with a priority class used by the UE to
perform the first LBT procedure.
21. The UE of claim 13, wherein the processing circuitry is
operable to increment the LBT contention window size by
incrementing LBT contention window sizes associated with all
priority classes used by the UE.
22. The UE of claim 13, wherein the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is incremented when the NDI associated with
each HARQ process identifier of the plurality of HARQ identifiers
indicates a retransmission.
23. The UE of claim 13, wherein the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is reset when at least one NDI associated
with a HARQ process identifier of the plurality of HARQ identifiers
indicates new data.
24. The UE of claim 13, wherein the processing circuitry is
operable to perform the second LBT procedure by performing a
Category 4 LBT for physical uplink shared channel (PUSCH)
transmission on a licensed assisted access (LAA) secondary
cell.
25. A method for use in a network node of signaling
listen-before-talk (LBT) parameters, the method comprising:
receiving a first burst of uplink subframes from a user equipment
(UE) after a first LBT procedure, each subframe of the first burst
of uplink subframes associated with one or more transport blocks,
and each transport block associated with a hybrid automatic repeat
request (HARQ) process identifier; determining a set of transport
blocks in the first burst of uplink subframes that were not
received successfully by the network node; and before scheduling
the UE with a second LBT procedure, scheduling the UE with a second
burst of uplink frames using all the HARQ process identifiers
associated with the transport blocks in the determined set of
transport blocks.
26. The method of claim 25, wherein determining the set of
transport blocks in the first burst of uplink subframes that were
not received successfully by the network node comprises:
determining a reference subframe based on the last subframe before
a received subframe in which at least one transport block was
received successfully; and wherein the set of transport blocks
includes the transport blocks in the reference subframe that were
not received successfully.
27. A network node operable to signal listen-before-talk (LBT)
parameters, the network node comprising processing circuitry
operable to: receive a first burst of uplink subframes from a user
equipment (UE) after a first LBT procedure, each subframe of the
first burst of uplink subframes associated with one or more
transport blocks, and each transport block associated with a hybrid
automatic repeat request (HARQ) process identifier; determine a set
of transport blocks in the first burst of uplink subframes that
were not received successfully by the network node; and before
scheduling the UE with a second LBT procedure, schedule the UE with
a second burst of uplink frames using all the HARQ process
identifiers associated with the transport blocks in the determined
set of transport blocks.
28. The network node of claim 27, wherein the processing circuitry
operable to determine the set of transport blocks in the first
burst of uplink subframes that were not received successfully by
the network node is operable to: determine a reference subframe
based on the last subframe before a received subframe in which at
least one transport block was received successfully; and wherein
the set of transport blocks includes the transport blocks in the
reference subframe that were not received successfully.
29-30. (canceled)
Description
TECHNICAL FIELD
[0001] Particular embodiments are directed to wireless
communications and, more particularly, to methods and apparatus for
signaling and management of listen-before-talk (LBT) parameters for
uplink transmission in unlicensed spectrum.
INTRODUCTION
[0002] The Third Generation Partnership Project (3GPP) initiative
referred to as License Assisted Access (LAA) enables long term
evolution (LTE) equipment to operate in the unlicensed 5 GHz radio
spectrum. The unlicensed 5 GHz spectrum is used as a complement to
the licensed spectrum. Accordingly, devices connect in the licensed
spectrum (primary cell or PCell) and use carrier aggregation to
benefit from additional transmission capacity in the unlicensed
spectrum (secondary cell or SCell). To reduce the changes required
for aggregating licensed and unlicensed spectrum, the LTE frame
timing in the primary cell is simultaneously used in the secondary
cell.
[0003] The standalone LTE-U forum and 3GPP Rel-14 work item on
Uplink Licensed-Assisted Access (LAA) may specify that LTE user
equipment (UEs) may transmit on the uplink in the unlicensed 5 GHz
or license-shared 3.5 GHz radio spectrum. For the case of
standalone LTE-U, all downlink and uplink transmissions take place
entirely on the unlicensed spectrum.
[0004] Regulatory requirements may not permit transmissions in the
unlicensed spectrum without prior channel sensing. This is because
the unlicensed spectrum is shared with radios of similar or
dissimilar wireless technologies. Wireless devices may perform
channel sensing using a listen-before-talk (LBT) method. The LBT
method includes sensing the transmission medium for a pre-defined
minimum amount of time and backing off if the channel is busy.
[0005] Wi-Fi, LAA and Standalone LTE-U may operate in multi-carrier
mode with simultaneous transmission across multiple unlicensed
channels in the 5 GHz band. Wi-Fi follows a hierarchical
multi-carrier LBT scheme across multiple carriers which are
selected using specific channel bonding rules.
[0006] For LAA and Standalone LTE-U, uplink transmissions are
explicitly scheduled by the eNB, which has full control over when
UEs are allowed to transmit. For carriers operating in unlicensed
spectrum, however, UEs perform a form of LBT before transmitting on
the carrier. The form of LBT may depend on the number of UEs that
are scheduled, the number of subframes that are scheduled in
succession, the length of the previous transmissions on the
carrier, and/or other such factors. Some parameters related to LBT
may be signaled by the eNB to UEs so that the UEs may perform LBT
before transmission. The signaling parameters, however, do not
fully encompass all the use cases and problems that may be
encountered for uplink transmissions in unlicensed spectrum.
[0007] Particular embodiments described below include more
signaling methods to solve these problems and address the new use
cases. In addition, the particular embodiments describe signaling
parameters that may be used to increase efficiency of LTE in
unlicensed spectrum.
[0008] As background, LTE uses OFDM in the downlink and discrete
Fourier transform (DFT)-spread OFDM (also referred to as
single-carrier FDMA) in the uplink. The basic LTE downlink physical
resource comprises a time-frequency grid as illustrated in FIG.
1.
[0009] FIG. 1 illustrates an example OFDM symbol. The horizontal
axis represents time and the other axis represents frequency. Each
resource element corresponds to one OFDM subcarrier during one OFDM
symbol interval. An uplink subframe has the same subcarrier spacing
as the downlink and the same number of SC-FDMA symbols in the time
domain as OFDM symbols in the downlink. In the time domain, LTE
downlink transmissions are organized into radio frames.
[0010] FIG. 2 illustrates an example radio frame. Each radio frame
is 10 ms and consists of ten equally-sized subframes of length
Tsubframe=1 ms. For normal cyclic prefix, one subframe consists of
14 OFDM symbols. The duration of each symbol is approximately 71.4
.mu.s.
[0011] Resource allocation in LTE is typically described in terms
of resource blocks, where a resource block corresponds to one slot
(0.5 ms) in the time domain and 12 contiguous subcarriers in the
frequency domain. A pair of two adjacent resource blocks in time
direction (1.0 ms) is known as a resource block pair. Resource
blocks are numbered in the frequency domain, starting with 0 from
one end of the system bandwidth.
[0012] Downlink transmissions are dynamically scheduled. In each
subframe a base station transmits control information about which
terminals data is transmitted to and upon which resource blocks the
data is transmitted in the current downlink subframe. This control
signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM
symbols in each subframe and the number n=1, 2, 3 or 4 is known as
the Control Format Indicator (CFI). The downlink subframe also
contains common reference symbols, which are known to the receiver
and used for coherent demodulation of e.g. the control
information.
[0013] FIG. 3 illustrates an example downlink subframe. The
subframe includes reference symbols and control signaling. In the
illustrated example, the control region includes 3 OFDM symbols
(i.e., CFI=3). The reference symbols include cell specific
reference symbols (CRS), which may support multiple functions
including fine time and frequency synchronization and channel
estimation for certain transmission modes.
[0014] For LTE Rel-8 to Rel-10, a base station schedules downlink
transmissions using a Physical Downlink Control Channel (PDCCH).
From LTE Rel-11 and onwards, downlink transmissions may also be
scheduled on an Enhanced Physical Downlink Control Channel
(EPDCCH).
[0015] The PDCCH/EPDCCH carries downlink control information (DCI)
such as scheduling decisions and power-control commands. For
example, the DCI includes downlink scheduling assignments such as
Physical Downlink Shared Channel (PDSCH) resource indication,
transport format, hybrid-ARQ information, and control information
related to spatial multiplexing (if applicable). A downlink
scheduling assignment also includes a command for power control of
the Physical Uplink Control Channel (PUCCH) used for transmission
of hybrid-ARQ (HARD) acknowledgements in response to downlink
scheduling assignments. The DCI may also include uplink scheduling
grants such as Physical Uplink Shared Channel (PUSCH) resource
indication, transport format, and hybrid-ARQ-related information.
An uplink scheduling grant also includes a command for power
control of the PUSCH. The DCI may also include power control
commands for a set of terminals as a complement to the commands
included in the scheduling assignments/grants.
[0016] One PDCCH/EPDCCH carries one DCI message containing one of
the groups of information listed above. Because a base station may
schedule multiple terminals simultaneously, and each terminal may
be scheduled on both downlink and uplink simultaneously, multiple
scheduling messages may be transmitted within each subframe. Each
scheduling message is transmitted on separate PDCCH/EPDCCH
resources. Consequently, multiple simultaneous PDCCH/EPDCCH
transmissions are typically within each subframe in each cell.
Furthermore, support for different radio-channel conditions may use
link adaptation. In link adaptation the code rate of the
PDCCH/EPDCCH is selected by adapting the resource usage for the
PDCCH/EPDCCH to match the radio-channel conditions.
[0017] In LTE, the eNB transmits the uplink transmission scheduling
command to the UE. The LTE standard specifies a fixed delay between
the time the scheduling command is transmitted and the time the UE
transmits the uplink signal. This delay provides the UE time to
decode the PDCCH/EPDCCH and prepare the uplink signal for
transmission. For a frequency division duplex (FDD) serving cell,
the uplink grant delay is 4 ms. For a time division duplex (TDD)
serving cell, the uplink grant delay can be greater than 4 ms.
[0018] The LTE Rel-10 standard and above supports bandwidths larger
than 20 MHz. One requirement of LTE Rel-10 is backward
compatibility with LTE Rel-8. This includes spectrum compatibility.
One way to provide compatibility is for an LTE Rel-10 carrier wider
than 20 MHz to appear as a number of LTE carriers to an LTE Rel-8
terminal. Each such carrier may be referred to as a Component
Carrier (CC).
[0019] For early LTE Rel-10 deployments, the number of LTE
Rel-10-capable terminals will likely be smaller than the number of
LTE legacy terminals already in existence. Thus, efficient use of a
wide carrier is needed for legacy terminals, i.e. providing
carriers where legacy terminals may be scheduled in all parts of
the wideband LTE Rel-10 carrier. One solution uses carrier
aggregation. Using carrier aggregation, an LTE Rel-10 terminal may
receive multiple component carriers. The components carriers may
have the same structure as a Rel-8 carrier.
[0020] FIG. 4 illustrates an example of carrier aggregation. A
system bandwidth of 100 MHz may be represented by 5 component
carriers each with 20 MHz bandwidth. A UE capable of carrier
aggregation may be assigned a primary cell (PCell), which is always
activated, and one or more secondary cells (SCells) which may be
activated or deactivated dynamically.
[0021] The number of aggregated component carriers as well as the
bandwidth of the individual component carriers may be different for
uplink and downlink. A symmetric configuration refers to a
configuration where the number of component carriers in downlink is
the same as in uplink. An asymmetric configuration refers to a
configuration where the number of component carriers is different
between downlink and uplink. The number of component carriers
configured in a cell may be different from the number of component
carriers seen by a terminal. For example, a terminal may support
more downlink component carriers than uplink component carriers,
even though the cell is configured with the same number of uplink
and downlink component carriers.
[0022] Another feature of carrier aggregation is the ability to
perform cross-carrier scheduling. Cross-carrier scheduling enables
a (E)PDCCH on one component carrier to schedule data transmissions
on another component carrier using a 3-bit Carrier Indicator Field
(CIF) inserted at the beginning of the (E)PDCCH messages. For data
transmissions on a given component carrier, a UE expects to receive
scheduling messages on the (E)PDCCH of just one component carrier
(i.e., either the same component carrier, or a different component
carrier via cross-carrier scheduling). The mapping from (E)PDCCH to
PDSCH may be configured semi-statically.
[0023] Another wireless network technology that may share
unlicensed spectrum with LTE is a wireless local area network
(WLAN). Typical WLAN deployments use carrier sense multiple access
with collision avoidance (CSMA/CA) for medium access. This means
that the channel is sensed to perform a clear channel assessment
(CCA), and a transmission is initiated only if the channel is
determined to be idle. If the channel is determined to be busy,
then the transmission is deferred until the channel is idle. When
the range of several access points using the same frequency
overlap, all transmissions related to one access point might be
deferred when a transmission on the same frequency to or from
another access point which is within range is detected.
Effectively, if several access points are within range of each
other, they will need to share the channel in time, and the
throughput for the individual access points may be severely
degraded. A general illustration of the listen-before-talk (LBT)
mechanism on a single unlicensed channel is shown in FIG. 5.
[0024] FIG. 5 illustrates an example WLAN listen-before-talk
mechanism. In the case of single-channel LBT, after a first Wi-Fi
station transmits a data frame to a second Wi-Fi station, the
second station transmits an ACK frame back to the first station
with a delay of 16 .mu.s. The ACK frame is transmitted by the
second station without performing an LBT operation. To prevent
another station interfering with the ACK frame transmission, a
station defers for a duration of 34 .mu.s (referred to as DIFS)
after the channel is observed to be occupied before assessing again
whether the channel is occupied.
[0025] Thus, a station that wishes to transmit first performs a
clear channel assessment by sensing the medium for a fixed duration
DIFS. If the medium is idle, then the station assumes that it may
take ownership of the medium and begins a frame exchange sequence.
If the medium is busy, the station waits for the medium to go idle,
defers for DIFS, and waits for a further random backoff period. To
further prevent a station from occupying the channel continuously
and thereby preventing other stations from accessing the channel,
after a successful transmission, a station performs a random
backoff before transmitting again.
[0026] For multi-carrier operation, Wi-Fi uses a hierarchical
channel bonding scheme to determine its transmission bandwidth for
a frame, which could be 20 MHz, 40 MHz, 80 MHz, or 160 MHz, for
example. In the 5 GHz band, wider Wi-Fi channel widths of 40 MHz,
80 MHz, 160 MHz or 80+80 MHz are formed by combining 20 MHz
sub-channels in a non-overlapping manner. A pre-determined primary
channel performs the contention window-based random access
procedure after a defer period, if necessary, and then counts down
the random number generated. The secondary channels perform a quick
CCA check for a PIFS duration (generally 25 .mu.s) before the
potential start of transmission to determine if the additional
secondary channels are available for transmission. Based on the
results of the secondary CCA check, transmission is performed on
the larger bandwidths; otherwise transmission falls back to smaller
bandwidths. The Wi-Fi primary channel is always included in all
transmissions (i.e., transmission on secondary channels alone is
not allowed).
[0027] LTE has traditionally used dedicated frequency spectrum. An
advantage of dedicated spectrum is that an LTE system does not need
to coexist with other non-3GPP radio access technologies in the
same spectrum, which can maximize spectrum efficiency. The spectrum
allocated to LTE, however, is limited. It may not meet the ever
increasing demand for larger throughput from applications/services.
Therefore, 3GPP also specifies how LTE may use unlicensed spectrum
in addition to licensed spectrum. In addition, Standalone LTE-U is
under development by the MulteFire Alliance, in which LTE operates
solely in unlicensed spectrum.
[0028] FIG. 6 illustrates a user equipment with license assisted
access to unlicensed spectrum. In license assisted access, a UE is
connected to a PCell in the licensed band and one or more SCells in
the unlicensed band. A secondary cell in unlicensed spectrum may be
referred to as a LAA secondary cell (LAA SCell). The LAA SCell may
operate in downlink-only mode or operate with both uplink and
downlink traffic. In some scenarios, LTE nodes may operate in
standalone mode in license-exempt channels without assistance from
a licensed cell.
[0029] Unlicensed spectrum can, by definition, be used
simultaneously by multiple different technologies. Therefore, LAA
must coexist and cooperate with other systems, such as IEEE 802.11
(Wi-Fi). To coexist fairly with a Wi-Fi system, transmission on the
SCell conforms to LBT protocols to avoid collisions which may cause
severe interference to on-going transmissions. This includes both
performing LBT before commencing transmissions, and limiting the
maximum duration of a single transmission burst. The maximum
transmission burst duration is specified by country and
region-specific regulations (e.g., 4 ms in Japan and 13 ms
according to EN 301.893). An example is illustrated in FIG. 7.
[0030] FIG. 7 illustrates an example of uplink license assisted
access transmissions based on an uplink listen-before-talk
protocol. The example illustrates a duration of a transmission
burst on an LAA SCell constrained by a maximum allowed transmission
duration of 4 ms. For example, the illustration divides an 8 ms
occupancy time into 4 ms for downlink channel occupancy and 4 ms
for uplink channel occupancy.
[0031] Before the eNB transmits data in the downlink, it performs
LBT to gain channel access. During the eNB's transmission duration,
it also sends out control channels to schedule certain UEs to
transmit in the uplink at specific time later. After the eNB
releases the channel, the scheduled UEs perform LBT to determine
whether they can transmit in the channel at said specific time. For
example, after receiving a downlink transmission in subframes n-4
to n-1 (i.e., 4 ms), the UE performs a clear channel access for the
uplink at subframe n. If the channel is clear, the UE transmits in
uplink for subframes n to n+3 (i.e., 4 ms).
[0032] When an eNB obtains an opportunity to transmit in unlicensed
spectrum, the opportunity (also referred to as a transmit
opportunity (TXOP)), may be shared with UEs that the eNB is
serving. Transitions between transmissions from the eNB to
transmissions from UEs may be handled in two ways, one where the
UEs perform an LBT operation prior to transmission and one where
the UEs do not perform an LBT operation.
[0033] The case where an LBT operation is not performed will most
likely need the gap between downlink transmissions (from the eNB)
and uplink transmissions (from the UE(s)) to be no more than 16
.mu.s. When an LBT operation is to be performed for a particular
subframe, gaps will need to be inserted in the uplink subframes to
allow for the UE to perform a listen-before-talk operation without
being interfered by transmissions from other UEs in the same
serving cell. To avoid significantly degrading uplink throughput,
the gaps should not be too large. Therefore, the gap in an uplink
subframe of 14 DFT spread OFDM (DFTS-OFDM) symbols is likely to not
be larger than one DFTS-OFDM symbol, which is approximately 71
microseconds in duration.
[0034] Performing LBT may generally include two broad categories of
LBT operation. A first type uses an LBT procedure with full random
backoff similar to what is used by IEEE 802.11 compliant nodes.
These schemes are also referred to as Category 4 LBT schemes.
[0035] In these schemes a random backoff counter is drawn uniformly
randomly in the interval {0, CW}, where CW is the contention
window. The size of the contention window may be approximately
doubled every time a collision on the channel is detected. Thus,
this procedure may also be referred to as a binary exponential
backoff.
[0036] The contention window size is limited by a minimum value,
CWmin, and a maximum value, CWmax. The values of CWmin and CWmax
may vary depending on the priority class of the traffic. For the
highest priority class, the {CWmin, CWmax} values may be limited to
{3, 7} where these numbers are counted in increments of one slot
which has a duration of 9 microseconds as shown in FIG. 5. There
are four defined priority classes. The remaining three priority
classes use contention window size pairs of {7, 15}, {15, 63} and
{15, 1023}, respectively, for an access point (AP) or an eNB. For
Wi-Fi STAs or UEs in LTE, the values of {15, 63} are not used.
[0037] In the second type of LBT procedure, a UE may perform an LBT
operation for a fixed duration (e.g., 25 .mu.s). Generally, the
second type of LBT is preferable for transitions between downlink
and uplink transmissions, because it minimizes the probability of
another node completing its LBT operations and commencing
transmissions on the channel. Many situations, however, may need to
use a Category 4 LBT scheme.
[0038] One technique to minimize gaps between downlink and uplink
transmissions is to use a timing advance command to advance the
timing of the UEs transmissions on the uplink so that they occur
earlier. This technique may be used where the eNB may employ
transmissions only over a part of the subframe in the last downlink
subframe of a transmission burst. In this case, there is a gap
within the downlink subframe that can be occupied by uplink
transmissions by UEs that have received timing advance (TA)
commands.
[0039] The use of LTE carrier aggregation (CA), introduced in
Rel-10, may increase the peak data rate, system capacity, and user
experience by aggregating radio resources from multiple carriers
that may reside in the same band or different bands. Rel-13 LAA and
Standalone LTE-U offer an ability to operate on multiple carriers
in unlicensed spectrum simultaneously. The extension of the CA
framework beyond 5 carriers was completed in LTE Rel-13, which
supports up to 32 carriers in both uplink and downlink.
[0040] 3GPP specifications may include multi-subframe scheduling
for Rel-14 LAA where one or more uplink grants transmitted in a
single subframe can schedule uplink data in multiple subframes. The
parameters that are signaled as part of the multi-subframe
scheduling grant include hybrid ARQ acknowledgements (HARQ-ACKs)
and related parameters. Specifically, the grants include legacy
parameters (i.e., the new data indication (NDI), redundancy version
(RV), and the HARQ-ACK bits themselves, which generally consist of
one bit per transport block that is being acknowledged).
[0041] Signaling of LBT parameters for LAA may use both explicit
and implicit methods. The solutions include signaling of random
backoff parameters such as the random backoff counter, contention
window sizes, and the LBT priority class to be used. The signaling
of these parameters may vary depending on factors such as the load
and the set of UEs being multiplexed in a single subframe. Implicit
signaling of the LBT priority class to be used can be based on
various factors including the number of contiguous subframes that
have been scheduled to the UE. The contention window sizes to be
used at the UE can also be implicitly signaled by indicating
whether the transmission is a new transmission or a
retransmission.
[0042] Existing signaling and contention window management methods,
however, do not fully account for the problems that arise when
using implicit signaling to indicate contention window size that
the UE must use. When explicit signaling is used, it creates
unnecessarily large signaling overhead.
SUMMARY
[0043] The embodiments described herein include efficiently
signaling listen-before-talk (LBT) parameters for a Category 4 LBT
scheme to a user equipment (UE), while ensuring that requirements
on management of contention windows are met. Signaling to enable
the functionality is disclosed. In general, the contention window
adjustment is based on the radio conditions experienced during the
beginning of a transmission. For example, if the transmission after
a successful Category 4 LBT experiences collision, the
corresponding contention window size is increased for the next
Category 4 LBT attempt.
[0044] Some embodiments include implicit signaling with contention
window management at the UE with the following elements: (1) use of
the NDI bit for a HARQ process for which information is available
in a previously scheduled burst, and (2) use of a UE's knowledge of
the LBT failure or success for subframes of the previously
scheduled burst for the UE. The following embodiments include
managing the contention window size of a Category 4 LBT scheme used
by a UE in a particular uplink subframe.
[0045] According to some embodiments, a method for use in a user
equipment (UE) of managing a listen-before-talk (LBT) contention
window size comprises transmitting a first burst of uplink
subframes after a first LBT procedure. The LBT procedure is
performed using an LBT contention window size. The method further
comprises determining a reference subframe based on the first burst
of uplink subframes. The reference subframe is associated with a
reference hybrid automatic repeat request (HARQ) process
identifier. The method further comprises receiving scheduling for a
second burst of uplink subframes. The scheduling comprises, for
each subframe of the second burst of uplink subframes, an
associated HARQ process identifier and an associated new data
indicator (NDI). When the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates new data, the method resets the
LBT contention window size to a minimum value. When the UE
determines the HARQ process identifier associated with at least one
of the subframes of the second burst of uplink subframes matches
the reference HARQ process identifier and the associated NDI
indicates a retransmission, the method increments the LBT
contention window size. The method further comprises performing a
second LBT procedure using the contention window size.
[0046] In particular embodiments, determining the reference
subframe comprises determining a most recently transmitted uplink
subframe in the first burst of uplink subframes for which the
associated HARQ process identifier is also found in the received
scheduling for the second burst of uplink subframes.
[0047] In particular embodiments, determining the reference
subframe comprises determining the first transmitted subframe of
the first burst of uplink subframes for which the HARQ process
identifier associated with the first subframe of the first burst of
uplink subframes is also found in the received scheduling for the
second burst of uplink subframes.
[0048] In particular embodiments, transmission of the first burst
ended more than a threshold time (e.g., 4 ms) prior to determining
the reference subframe.
[0049] In particular embodiments, resetting the LBT contention
window size to a minimum value comprises resetting the LBT
contention window size to a minimum value of a set of values
associated with a priority class used by the UE to perform the
first LBT procedure. Resetting the LBT contention window size to a
minimum value may comprise resetting LBT contention window sizes
associated with all priority classes used by the UE.
[0050] In particular embodiments, incrementing the LBT contention
window size comprises incrementing the LBT contention window size
to a next value in a set of values associated with a priority class
used by the UE to perform the first LBT procedure. Incrementing the
LBT contention window size may comprise incrementing LBT contention
window sizes associated with all priority classes used by the
UE.
[0051] In particular embodiments, the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is incremented when the NDI associated with
each HARQ process identifier of the plurality of HARQ identifiers
indicates a retransmission. In some embodiments, the LBT contention
window size is reset when at least one NDI associated with a HARQ
process identifier of the plurality of HARQ identifiers indicates
new data.
[0052] In particular embodiments, performing the second LBT
procedure comprises performing a Category 4 LBT for physical uplink
shared channel (PUSCH) transmission on a licensed assisted access
(LAA) secondary cell.
[0053] According to some embodiments, a UE capable of managing a
LBT contention window size comprises processing circuitry operable
to transmit a first burst of uplink subframes after a first LBT
procedure. The LBT procedure is performed using an LBT contention
window size. The processing circuitry is further operable to
determine a reference subframe based on the first burst of uplink
subframes. The reference subframe is associated with a reference
HARQ process identifier. The processing circuitry is further
operable to receive scheduling for a second burst of uplink
subframes. The scheduling comprises, for each subframe of the
second burst of uplink subframes, an associated HARQ process
identifier and an associated NDI. When the UE determines the HARQ
process identifier associated with at least one of the subframes of
the second burst of uplink subframes matches the reference HARQ
process identifier and the associated NDI indicates new data, the
processing circuitry is operable to reset the LBT contention window
size to a minimum value. When the UE determines the HARQ process
identifier associated with at least one of the subframes of the
second burst of uplink subframes matches the reference HARQ process
identifier and the associated NDI indicates a retransmission, the
processing circuitry is operable to increment the LBT contention
window size. The processing circuitry is further operable to
perform a second LBT procedure using the contention window
size.
[0054] In particular embodiments, the processing circuitry is
operable to determine the reference subframe by determining a most
recently transmitted uplink subframe in the first burst of uplink
subframes for which the associated HARQ process identifier is also
found in the received scheduling for the second burst of uplink
subframes.
[0055] In particular embodiments, the processing circuitry is
operable to determine the reference subframe by determining the
first transmitted subframe of the first burst of uplink subframes
for which the HARQ process identifier associated with the first
subframe of the first burst of uplink subframes is also found in
the received scheduling for the second burst of uplink
subframes.
[0056] In particular embodiments, transmission of the first burst
ended more than a threshold time (e.g., 4 ms) prior to determining
the reference subframe.
[0057] In particular embodiments, the processing circuitry is
operable to reset the LBT contention window size to a minimum value
by resetting the LBT contention window size to a minimum value of a
set of values associated with a priority class used by the UE to
perform the first LBT procedure. In some embodiments, the
processing circuitry is operable to reset the LBT contention window
size to a minimum value by resetting LBT contention window sizes
associated with all priority classes used by the UE.
[0058] In particular embodiments, the processing circuitry is
operable to increment the LBT contention window size by
incrementing the LBT contention window size to a next value in a
set of values associated with a priority class used by the UE to
perform the first LBT procedure. In some embodiments, the
processing circuitry is operable to increment the LBT contention
window size by incrementing LBT contention window sizes associated
with all priority classes used by the UE.
[0059] In particular embodiments, the reference subframe is
associated with a plurality of HARQ process identifiers and the LBT
contention window size is incremented when the NDI associated with
each HARQ process identifier of the plurality of HARQ identifiers
indicates a retransmission. In some embodiments, the LBT contention
window size is reset when at least one NDI associated with a HARQ
process identifier of the plurality of HARQ identifiers indicates
new data.
[0060] In particular embodiments, the processing circuitry is
operable to perform the second LBT procedure by performing a
Category 4 LBT for PUSCH transmission on a LAA secondary cell.
[0061] According to some embodiments, a method for use in a network
node of signaling LBT parameters comprises receiving a first burst
of uplink subframes from a UE after a first LBT procedure. Each
subframe of the first burst of uplink subframes is associated with
one or more transport blocks, and each transport block is
associated with a HARQ process identifier. The method further
comprises determining a set of transport blocks in the first burst
of uplink subframes that were not received successfully by the
network node. Before scheduling the UE with a second LBT procedure,
the method further comprises scheduling the UE with a second burst
of uplink frames using all the HARQ process identifiers associated
with the transport blocks in the determined set of transport
blocks.
[0062] In particular embodiments, determining the set of transport
blocks in the first burst of uplink subframes that were not
received successfully by the network node comprises determining a
reference subframe based on the last subframe before a received
subframe in which at least one transport block was received
successfully. The set of transport blocks includes the transport
blocks in the reference subframe that were not received
successfully.
[0063] According to some embodiments, a network node operable to
signal LBT parameters comprises processing circuitry operable to
receive a first burst of uplink subframes from a UE after a first
LBT procedure. Each subframe of the first burst of uplink subframes
is associated with one or more transport blocks, and each transport
block is associated with a HARQ process identifier. The processing
circuitry is further operable to determine a set of transport
blocks in the first burst of uplink subframes that were not
received successfully by the network node. Before scheduling the UE
with a second LBT procedure, the processing circuitry is further
operable to schedule the UE with a second burst of uplink frames
using all the HARQ process identifiers associated with the
transport blocks in the determined set of transport blocks.
[0064] In particular embodiments, the processing circuitry is
operable to determine a reference subframe based on the last
subframe before a received subframe in which at least one transport
block was received successfully. The set of transport blocks
includes the transport blocks in the reference subframe that were
not received successfully.
[0065] According to some embodiments, a UE capable of managing a
LBT contention window size comprises a transmitting module, a
determining module, a receiving module, and an LBT module. The
transmitting module is operable to transmit a first burst of uplink
subframes after a first LBT procedure. The LBT procedure is
performed using an LBT contention window size. The determining
module operable to determine a reference subframe based on the
first burst of uplink subframes. The reference subframe is
associated with a reference HARQ process identifier. The receiving
module is operable to receive scheduling for a second burst of
uplink subframes. The scheduling comprises, for each subframe of
the second burst of uplink subframes, an associated HARQ process
identifier and an associated NDI. When the UE determines the HARQ
process identifier associated with at least one of the subframes of
the second burst of uplink subframes matches the reference HARQ
process identifier and the associated NDI indicates new data, the
LBT module is operable to reset the LBT contention window size to a
minimum value. When the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates a retransmission, the LBT module
is operable to increment the LBT contention window size. The LBT
module is further operable to perform a second LBT procedure using
the contention window size.
[0066] According to some embodiments, a network node operable to
signal LBT parameters comprises a receiving module, a determining
module, and an LBT module. The receiving module is operable to
receive a first burst of uplink subframes from a UE after a first
LBT procedure. Each subframe of the first burst of uplink subframes
is associated with one or more transport blocks, and each transport
block is associated with a HARQ process identifier. The determining
module is operable to determine a set of transport blocks in the
first burst of uplink subframes that were not received successfully
by the network node. Before scheduling the UE with a second LBT
procedure, the LBT module is operable to schedule the UE with a
second burst of uplink frames using all the HARQ process
identifiers associated with the transport blocks in the determined
set of transport blocks.
[0067] Also disclosed is a computer program product. The computer
program product comprises instructions stored on non-transient
computer-readable media which, when executed by a processor,
perform the act of transmitting a first burst of uplink subframes
after a first LBT procedure. The LBT procedure is performed using
an LBT contention window size. The instructions are further
operable to perform the act of determining a reference subframe
based on the first burst of uplink subframes. The reference
subframe is associated with a reference hybrid automatic repeat
request (HARQ) process identifier. The instructions are further
operable to perform the act of receiving scheduling for a second
burst of uplink subframes. The scheduling comprises, for each
subframe of the second burst of uplink subframes, an associated
HARQ process identifier and an associated new data indicator (NDI).
When the UE determines the HARQ process identifier associated with
at least one of the subframes of the second burst of uplink
subframes matches the reference HARQ process identifier and the
associated NDI indicates new data, the instructions are further
operable to perform the act of resetting the LBT contention window
size to a minimum value. When the UE determines the HARQ process
identifier associated with at least one of the subframes of the
second burst of uplink subframes matches the reference HARQ process
identifier and the associated NDI indicates a retransmission, the
instructions are further operable to perform the act of
incrementing the LBT contention window size. The instructions are
further operable to perform the act of performing a second LBT
procedure using the contention window size.
[0068] Another computer program product comprises instructions
stored on non-transient computer-readable media which, when
executed by a processor, perform the act of receiving a first burst
of uplink subframes from a UE after a first LBT procedure. Each
subframe of the first burst of uplink subframes is associated with
one or more transport blocks, and each transport block is
associated with a HARQ process identifier. The instructions are
further operable to perform the act of determining a set of
transport blocks in the first burst of uplink subframes that were
not received successfully by the network node. Before scheduling
the UE with a second LBT procedure, the instructions are further
operable to perform the act of scheduling the UE with a second
burst of uplink frames using all the HARQ process identifiers
associated with the transport blocks in the determined set of
transport blocks.
[0069] Particular embodiments may exhibit some of the following
technical advantages. For example, particular embodiments may
improve uplink and/or system performance by reducing the amount of
signaling, which may reduce network load and device complexity. In
some embodiments, a network node may closely track the contention
window adjustment at the wireless device. Other technical
advantages will be readily apparent to one skilled in the art from
the following figures, description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] For a more complete understanding of the embodiments and
their features and advantages, reference is now made to the
following description, taken in conjunction with the accompanying
drawings, in which:
[0071] FIG. 1 illustrates an example OFDM symbol;
[0072] FIG. 2 illustrates an example radio frame;
[0073] FIG. 3 illustrates an example downlink subframe;
[0074] FIG. 4 illustrates an example of carrier aggregation;
[0075] FIG. 5 illustrates an example WLAN listen-before-talk
mechanism;
[0076] FIG. 6 illustrates a user equipment with license assisted
access to unlicensed spectrum;
[0077] FIG. 7 illustrates an example of uplink license assisted
access transmissions based on an uplink listen-before-talk
protocol;
[0078] FIG. 8 is a block diagram illustrating an example wireless
network, according to some embodiments;
[0079] FIGS. 9-12 illustrate example sequences of subframes for
implicitly determining an LBT contention window size, according to
some embodiments;
[0080] FIG. 13 is a flow diagram illustrating an example method in
a user equipment, according to some embodiments;
[0081] FIG. 14 is a flow diagram illustrating an example method in
a network node, according to some embodiments;
[0082] FIG. 15A is a block diagram illustrating an example
embodiment of a wireless device;
[0083] FIG. 15B is a block diagram illustrating example components
of a wireless device;
[0084] FIG. 16A is a block diagram illustrating an example
embodiment of a network node; and
[0085] FIG. 16B is a block diagram illustrating example components
of a network node.
DETAILED DESCRIPTION
[0086] Long term evolution (LTE) equipment may operate in the
unlicensed 5 GHz radio spectrum according to the Third Generation
Partnership Project (3GPP) initiative referred to as License
Assisted Access (LAA). The unlicensed 5 GHz spectrum is used as a
complement to the licensed spectrum. Accordingly, devices connect
in the licensed spectrum (primary cell or PCell) and use carrier
aggregation to benefit from additional transmission capacity in the
unlicensed spectrum (secondary cell or SCell).
[0087] Regulatory requirements may not permit transmissions in the
unlicensed spectrum without prior channel sensing. Wireless devices
may perform channel sensing using a listen-before-talk (LBT)
method. The LBT method includes sensing the transmission
[0088] The form of LBT may depend on the number of UEs that are
scheduled, the number of subframes that are scheduled in
succession, the length of the previous transmissions on the
carrier, and/or other such factors. Some parameters related to LBT
may be signaled by the eNB to UEs so that the UEs may perform LBT
before transmission. The signaling parameters, however, do not
fully encompass all the use cases and problems that may be
encountered for uplink transmissions in unlicensed spectrum.
[0089] Before an eNB transmits data in the downlink, it performs
LBT to gain channel access. During the eNB's transmission duration,
it also sends out control channels to schedule certain UEs to
transmit in the uplink at specific time later. After the eNB
releases the channel, the scheduled UEs perform LBT to determine
whether they can transmit in the channel at said specific time.
[0090] Performing LBT may generally include two broad categories of
LBT operation. A first type uses an LBT procedure with full random
backoff similar to what is used by IEEE 802.11 compliant nodes.
These schemes are also referred to as Category 4 LBT schemes.
[0091] In these schemes a random backoff counter is drawn uniformly
randomly in the interval {0, CW}, where CW is the contention
window. The size of the contention window may be approximately
doubled every time a collision on the channel is detected. Thus,
this procedure may also be referred to as a binary exponential
backoff.
[0092] The contention window size is limited by a minimum value,
CWmin, and a maximum value, CWmax. The values of CWmin and CWmax
may vary depending on the priority class of the traffic.
[0093] In the second type of LBT procedure, a UE may perform an LBT
operation for a fixed duration (e.g., 25 .mu.s). Generally, the
second type of LBT is preferable for transitions between downlink
and uplink transmissions, because it minimizes the probability of
another node completing its LBT operations and commencing
transmissions on the channel. Many situations, however, may need to
use a Category 4 LBT scheme.
[0094] 3GPP specifications may include multi-subframe scheduling
for Rel-14 LAA where one or more uplink grants transmitted in a
single subframe can schedule uplink data in multiple subframes. The
parameters that are signaled as part of the multi-subframe
scheduling grant include hybrid ARQ acknowledgements (HARQ-ACKs)
and related parameters. Specifically, the grants include legacy
parameters (i.e., the new data indication (NDI), redundancy version
(RV), and the HARQ-ACK bits themselves, which generally consist of
one bit per transport block that is being acknowledged).
[0095] Signaling of LBT parameters for LAA may use both explicit
and implicit methods. The solutions include signaling of random
backoff parameters such as the random backoff counter, contention
window sizes, and the LBT priority class to be used. The signaling
of these parameters may vary depending on factors such as the load
and the set of UEs being multiplexed in a single subframe. Implicit
signaling of the LBT priority class to be used can be based on
various factors including the number of contiguous subframes that
have been scheduled to the UE. The contention window sizes to be
used at the UE can also be implicitly signaled by indicating
whether the transmission is a new transmission or a
retransmission.
[0096] Existing signaling and contention window management methods,
however, do not fully account for the problems that arise when
using implicit signaling to indicate contention window size that
the UE must use. When explicit signaling is used, it creates
unnecessarily large signaling overhead. In consideration of these
issues, certain embodiments efficiently signal LBT parameters for a
Category 4 LBT scheme to a UE, while meeting the requirements for
management of contention windows.
[0097] In general, the contention window adjustment is based on the
radio conditions experienced at the beginning of a transmission.
For example, if the transmission after a successful Category 4 LBT
experiences collision, the corresponding contention window size is
increased for the next Category 4 LBT attempt. However,
conventional signaling and contention window management methods
which are adopted at the UE or at the eNB suffer from the
misinterpretation in the available information at the other side.
If the UE fails in LBT and does not transmit anything, or if the UE
transmits, but the transmission is heavily interfered with, then
the eNB fails to detect a valid transmission from the UE. The eNB
cannot distinguish between transmission failure and transmission
with collision, where only the latter should contribute to the
contention window adjustment.
[0098] Particular embodiments obviate the problems described above
and include adjusting LBT parameters, such as a contention window
size for a Category 4 LBT scheme, using implicit signaling provided
by an eNB and the UEs knowledge of its transmission. The following
general embodiments for managing the contention window size of a
Category 4 LBT scheme used by a UE in a particular uplink subframe
are described.
[0099] Some embodiments include implicit signaling with contention
window management at the UE. For example, particular embodiments
use a new data indicator (NDI) bit for a hybrid automatic repeat
request (HARM) process for which information is available in a
previously scheduled burst. Particular embodiments may also use a
UE's knowledge of the LBT failure or success for subframes of the
previously scheduled burst for the UE.
[0100] Particular embodiments may improve uplink and/or system
performance by reducing the amount of signaling, which may reduce
network load and device complexity. No additional signaling
overhead is needed to manage the contention window size. An eNB can
closely track the contention window adjustment at the UE.
[0101] The embodiments described herein are applicable to both LAA
LTE and standalone LTE-U operation, and in general for any system
such as LTE operating in unlicensed spectrum or any spectrum where
listen-before-talk protocols are used and where there is some fixed
timing where transmissions occur.
[0102] The following description sets forth numerous specific
details. It is understood, however, that embodiments may be
practiced without these specific details. In other instances,
well-known circuits, structures and techniques have not been shown
in detail in order not to obscure the understanding of this
description. Those of ordinary skill in the art, with the included
descriptions, will be able to implement appropriate functionality
without undue experimentation.
[0103] References in the specification to "one embodiment," "an
embodiment," "an example embodiment," etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art to implement such
feature, structure, or characteristic in connection with other
embodiments, whether or not explicitly described.
[0104] Particular embodiments are described with reference to FIGS.
8-16B of the drawings, like numerals being used for like and
corresponding parts of the various drawings. LTE is used throughout
this disclosure as an example cellular system, but the ideas
presented herein may apply to other wireless communication systems
as well.
[0105] FIG. 8 is a block diagram illustrating an example wireless
network, according to a particular embodiment. Wireless network 100
includes one or more wireless devices 110 (such as mobile phones,
smart phones, laptop computers, tablet computers, MTC devices, or
any other devices that can provide wireless communication) and a
plurality of network nodes 120 (such as base stations or eNodeBs).
Wireless device 110 may also be referred to as a UE. Network node
120 serves coverage area 115 (also referred to as cell 115).
[0106] In general, wireless devices 110 that are within coverage of
network node 120 (e.g., within cell 115 served by network node 120)
communicate with network node 120 by transmitting and receiving
wireless signals 130. For example, wireless devices 110 and network
node 120 may communicate wireless signals 130 containing voice
traffic, data traffic, and/or control signals. A network node 120
communicating voice traffic, data traffic, and/or control signals
to wireless device 110 may be referred to as a serving network node
120 for the wireless device 110. Communication between wireless
device 110 and network node 120 may be referred to as cellular
communication. Wireless signals 130 may include both downlink
transmissions (from network node 120 to wireless devices 110) and
uplink transmissions (from wireless devices 110 to network node
120).
[0107] Each network node 120 may have a single transmitter or
multiple transmitters for transmitting signals 130 to wireless
devices 110. In some embodiments, network node 120 may comprise a
multi-input multi-output (MIMO) system. Similarly, each wireless
device 110 may have a single receiver or multiple receivers for
receiving signals 130 from network nodes 120 or other wireless
devices 110.
[0108] Wireless signals 130 may include frames and subframes, such
as those described with respect to FIGS. 1-3. Network node 120 may
dynamically schedule subframes as an uplink subframe, a downlink
subframe, or a combination uplink and downlink subframe.
[0109] Network node 120 may operate in a licensed frequency
spectrum, such as an LTE spectrum. Network node 120 may also
operate in an unlicensed frequency spectrum, such as a 5 GHz Wi-Fi
spectrum. In an unlicensed frequency spectrum, network node 120 may
coexist with other devices such as IEEE 802.11 access points and
terminals. To share the unlicensed spectrum, network node 120 may
perform LBT protocols before transmitting or receiving wireless
signals 130. Wireless device 110 may also operate in one or both of
licensed or unlicensed spectrum and in some embodiments may also
perform LBT protocols before transmitting wireless signals 130.
Both network node 120 and wireless device 110 may also operate in
licensed shared spectrum.
[0110] For example, network node 120a may operate in a licensed
spectrum and network node 120b may operate in an unlicensed
spectrum. Wireless device 110 may operate in both licensed and
unlicensed spectrum. In particular embodiments, network nodes 120a
and 120b may be configurable to operate in a licensed spectrum, an
unlicensed spectrum, a licensed shared spectrum, or any
combination. Although the coverage area of cell 115b is illustrated
as included in the coverage area of cell 115a, in particular
embodiments the coverage areas of cells 115a and 115b may overlap
partially, or may not overlap at all.
[0111] In particular embodiments, wireless device 110 and network
nodes 120 may perform carrier aggregation. For example, network
node 120a may serve wireless device 110 as a PCell and network node
120b may serve wireless device 110 as a SCell. Network nodes 120
may perform self-scheduling or cross-scheduling. If network node
120a is operating in licensed spectrum and network node 120b is
operating in unlicensed spectrum, network node 120a may provide
license assisted access to the unlicensed spectrum (i.e., network
node 120a is a LAA PCell and network node 120b is a LAA SCell).
[0112] In particular embodiments, network node 120a may dynamically
schedule uplink and downlink subframes for wireless device 110. For
example, in particular embodiments network node 120a may determine
a first uplink/downlink scheduling pattern for a first plurality of
consecutive subframes. Network node 120a may transmit the first
uplink/downlink scheduling pattern to wireless device 110 (e.g.,
using (E)PDCCH) and transmit at least one subframe to wireless
device 110 according to the first uplink/downlink scheduling
pattern.
[0113] If network node 120a received additional downlink data, or a
request for uplink transmission from a wireless device, for
example, then network node 120a may determine a second
uplink/downlink scheduling pattern for a second plurality of
consecutive subframes. Network node 120a may transmit the second
uplink/downlink scheduling pattern to wireless device 110 in any of
the subframes previously scheduled for wireless device 110.
[0114] In particular embodiments, the uplink/downlink scheduling
pattern may comprise a number of subsequent downlink subframes, a
number of subsequent downlink and uplink subframes, an indication
of which subframes to monitor or not monitor for downlink, or any
other suitable pattern.
[0115] In particular embodiments, wireless device 110 may receive,
from network node 120 (e.g., using (E)PDCCH), a first
uplink/downlink scheduling pattern for a first plurality of
consecutive subframes. Wireless device 110 may receive at least one
subframe according to the first uplink/downlink scheduling pattern.
In one of the scheduled downlink subframes, wireless device 110 may
receive a second uplink/downlink scheduling pattern for a second
plurality of consecutive subframes.
[0116] Wireless device 110 may perform LBT procedures before
transmitting in the uplink. For example, wireless device 110 may
transmit a first burst of uplink subframes after a first LBT
procedure. Wireless device 110 determines a reference subframe
based on the first burst of uplink subframes. The reference
subframe is associated with a reference HARQ process identifier.
Wireless device 110 receives scheduling for a second burst of
uplink subframes. The scheduling comprises, for each subframe of
the second burst of uplink subframes, an associated HARQ process
identifier and an associated NDI. When wireless device 110
determines the HARQ process identifier associated with at least one
of the subframes of the second burst of uplink subframes matches
the reference HARQ process identifier and the associated NDI
indicates new data, wireless device 110 resets the LBT contention
window size to a minimum value. When wireless device 110 determines
the HARQ process identifier associated with at least one of the
subframes of the second burst of uplink subframes matches the
reference HARQ process identifier and the associated NDI indicates
a retransmission, Wireless device 110 increments the LBT contention
window size. Wireless device 110 performs a second LBT procedure
using the contention window size.
[0117] In particular embodiments, wireless device 110 may determine
the reference subframe by determining a most recently transmitted
uplink subframe in the first burst of uplink subframes for which
the associated HARQ process identifier is also found in the
received scheduling for the second burst of uplink subframes. In
some embodiments, wireless device 110 may determine the reference
subframe by determining the first transmitted subframe of the first
burst of uplink subframes for which the HARQ process identifier
associated with the first subframe of the first burst of uplink
subframes is also found in the received scheduling for the second
burst of uplink subframes.
[0118] In particular embodiments, performing the second LBT
procedure comprises performing a Category 4 LBT for physical uplink
shared channel (PUSCH) transmission on a licensed assisted access
(LAA) secondary cell.
[0119] According to some embodiments, network node 120 may receive
a first burst of uplink subframes from wireless device 110 after a
first LBT procedure. Each subframe of the first burst of uplink
subframes is associated with one or more transport blocks, and each
transport block is associated with a HARQ process identifier.
Network node 120 determines a set of transport blocks in the first
burst of uplink subframes that were not received successfully.
Before scheduling wireless device 110 with a second LBT procedure,
network node 120 schedules wireless device 110 with a second burst
of uplink frames using all the HARQ process identifiers associated
with the transport blocks in the determined set of transport
blocks.
[0120] In particular embodiments, network node 120 determines a
reference subframe based on the last subframe before a received
subframe in which at least one transport block was received
successfully. The set of transport blocks includes the transport
blocks in the reference subframe that were not received
successfully.
[0121] Although particular embodiments are described with respect
to licensed or unlicensed spectrum, license assisted access, and/or
carrier aggregation, the embodiments described herein apply equally
to uplink and downlink scheduling in any spectrum and with respect
to a single cell or any combination of cells.
[0122] In wireless network 100, each network node 120 may use any
suitable radio access technology, such as long term evolution
(LTE), LTE-Advanced, UMTS, HSPA, GSM, cdma2000, NR, WiMax, WiFi,
and/or other suitable radio access technology. Wireless network 100
may include any suitable combination of one or more radio access
technologies. For purposes of example, various embodiments may be
described within the context of certain radio access technologies.
However, the scope of the disclosure is not limited to the examples
and other embodiments could use different radio access
technologies.
[0123] As described above, embodiments of a wireless network may
include one or more wireless devices and one or more different
types of radio network nodes capable of communicating with the
wireless devices. The network may also include any additional
elements suitable to support communication between wireless devices
or between a wireless device and another communication device (such
as a landline telephone). A wireless device may include any
suitable combination of hardware and/or software. For example, in
particular embodiments, a wireless device, such as wireless device
110, may include the components described with respect to FIG. 15A
below. Similarly, a network node may include any suitable
combination of hardware and/or software. For example, in particular
embodiments, a network node, such as network node 120, may include
the components described with respect to FIG. 16A below.
[0124] Some embodiments include implicit signaling with contention
window management at the UE. In general, the UE increases or resets
the contention window size based on the most recent HARQ feedback
information available for transport blocks that are transmitted at
the beginning of an uplink burst of subframes from the UE. The UE
knows whether the current grant is a transmission of a new
transport block or a retransmission as indicated by the new data
indicator (NDI) for transport blocks that are transmitted under a
given HARQ process. The eNB may use some number of HARQ processes
in parallel (e.g., 8 or 16). Certain UE procedures to achieve the
use of transport blocks in the first subframe of a transmission
burst in conjunction with implicit signaling from the eNB are
disclosed herein.
[0125] In particular embodiments, a UE may use the following
procedure to increase, or reset to the minimum value, the
contention window size for performing LBT prior to transmission of
an uplink burst for which the eNB has indicated that LBT using a
Category 4 random backoff procedure (where contention window sizes
can increase) should be performed. For example, the UE may use the
most recently transmitted burst of contiguous subframes (excluding
the currently scheduled burst) transmitted after a Category 4 LBT
procedure for which the HARQ process number used in the first
transmitted subframe of the burst also appears in a subsequently
scheduled burst as the reference transmission burst. The HARQ
process which satisfies the above condition is used as the
reference HARQ process to determine the contention window size.
[0126] After transmission of the reference subframe and reception
of a scheduling command for a subsequent burst that uses the
reference HARQ process, if the NDI bit for the reference HARQ
process is not toggled, indicating a retransmission, then the UE
increases the contention window size to the next higher value in
the set of contention window sizes for the priority class that was
used to perform LBT prior to transmission of the reference
transmission burst. In some embodiments, the contention window size
of all the LBT priority classes used by the UE are increased to the
next higher value.
[0127] If the NDI bit for the reference HARQ process is toggled,
indicating the transmission of a new transport block, the UE resets
the contention window size to the minimum value in the set of
contention window sizes for the priority class that is being used
by the UE to perform a Category 4 LBT procedure prior to
transmission of the next transmission burst. The priority class may
either be chosen by the UE based on the traffic type it intends to
transmit or may be indicated by the eNB in the uplink grants for
the next transmission burst. In some embodiments, the contention
window size of all the LBT priority classes used by the UE are
reset to the minimum value.
[0128] Particular embodiments includes procedures performed by an
eNB. In some embodiments, after reception of an uplink transmission
burst transmitted by a UE after a category 4 LBT procedure, the eNB
schedules data to the UE at or before the time a new transmission
burst is scheduled on the uplink using a Category 4 procedure using
all HARQ process identifiers in the received uplink transmission
burst for which the corresponding transport block was not
successfully received.
[0129] The HARQ process identifiers indicating retransmission need
not have been scheduled via uplink grant for a Category 4 LBT based
uplink transmission with random backoff. The processes may have
been scheduled via uplink grant for a short LBT (e.g., CCA of 25
us) or no LBT.
[0130] In examples described above, the contention window size is
increased to the next higher value only if the NDI bit for the
reference HARQ process is not toggled and the device actually
transmitted the reference HARQ process as the first subframe of the
prior transmission burst. This is because two types of reasons may
cause a HARQ process retransmission.
[0131] One reason is that the HARQ process was transmitted but
collision a happened. For these cases, a retransmission should use
a larger contention window size. Another reason is that the device
was not able to transmit the HARQ process in the prior scheduled
transmission burst based on the LBT protocol. That is, the device
observed occupied channel condition and refrained from transmission
to avoid collision. For these cases, the contention window size
should not be increased.
[0132] More detailed examples are described with respect to FIGS.
9-12. FIGS. 9-12 illustrate example sequences of subframes for
implicitly determining an LBT contention window size, according to
some embodiments.
[0133] FIG. 9 illustrates a first example sequence of subframes for
implicitly determining an LBT contention window size, according to
some embodiments. The illustrated example includes subframes
numbered N to N+19. Subframes N, N+1, N+2, and N+11 are downlink
subframes. Subframes N+4, N+6, N+7, N+8, N+9, N+15, N+16, N+17, and
N+19 are uplink subframes.
[0134] The uplink subframes are scheduled by grants received in the
downlink subframes. In the illustrated example, the arrows indicate
the downlink and uplink subframes where grants are transmitted in
the downlink subframes to schedule uplink data in the uplink
subframes. For example, downlink subframe N includes scheduling
grants for uplink subframes N+4, N+6, N+7, N+8, and N+9. Downlink
subframe N+11 includes scheduling grants for uplink subframes N+15,
N+16, N+17, and N+19.
[0135] The scheduling grant may indicate whether the uplink should
be performed after a Category 4 LBT procedure or a 25 us CCA. For
example, uplink subframes N+4, N+15, N+16, and N=17 are scheduled
for CCA. Uplink subframes N+6, N+7, N+8, N+9, and N+19 are
scheduled for Category 4 LBT.
[0136] In the illustrated example, each subframe includes two
transport blocks, and each transport block is associated with a
HARQ process (indicated by HARQ process identifiers H0, H1, H2,
etc.). Other embodiments may include any suitable number of
transport blocks and HARQ processes.
[0137] The scheduling information also includes a new data
indicator (NDI) that is represented by the tags N0 or N1. The tag
NO indicates that the new data indicator is toggled, which
indicates to the UE that the grant is for a new data transport
block. Similarly, N1 indicates that the new data indicator is
not-toggled, which means that the grant is for a retransmission of
a transport block that was incorrectly received.
[0138] As indicated by the legend in FIG. 9, some uplink subframes
may experience LBT failure (e.g., subframe N+6), a collision (e.g.,
subframe N+7), or a decoding error (e.g., subframe N+8). Note that
a decoding error may apply to one or both of the two transport
blocks for each subframe. The UE may use the HARQ process
identifiers to determine a reference subframe and the NDI to
determine whether to increment or reset an LBT contention window
size.
[0139] As a specific example with respect to FIG. 9, the uplink
grants in subframe N schedules the UE with PUSCH transmission in
subframe N+4 based on 25 us CCA and PUSCH transmission in subframes
N+6 to N+9 based on Category 4 LBT. The UE succeeds with CCA at
subframe N+4. The UE, however, fails with Category 4 LBT at
subframe N+6, but succeeds with Category 4 LBT at subframe N+7 and
continues transmission until subframe N+9.
[0140] The reference subframe for the UE is thus subframe N+7
(i.e., first transmitted uplink after a Category 4 LBT procedure)
and the corresponding HARQ process identifiers are H4 and H5. The
first transmitted subframe (N+7) happens to be heavily interfered
with in the example. At the eNB, transport blocks corresponding to
H2, H3, H4, and H5 are not detected and the transport block
corresponding to H6 is detected in error. The eNB schedules all
these HARQ processes (i.e., H2, H3, H4, H5 and H6) with non-toggled
NDI before granting the UE with another Category 4 LBT.
[0141] For contention window adjustment, the UE looks only for NDI
of H4 and H5 (i.e., the reference subframe) and finds that they are
non-toggled. Thus, the UE increases the contention window for the
next Category 4 LBT transmission. In the illustrated example, the
UE is scheduled for Category 4 LBT at subframe N+19. The UE
increases the contention window size before performing the Category
4 LBT at subframe N+19.
[0142] FIG. 10 illustrates another example sequence of subframes
for implicitly determining an LBT contention window size, according
to some embodiments. The illustrated example includes subframes
numbered N to N+19 similar to those described with respect to FIG.
9. A difference is that the uplink transmission at subframe N+7 is
successful in FIG. 10 (i.e., no collision as in FIG. 9).
[0143] The uplink grants in subframe N schedules the UE with PUSCH
transmission in subframe N+4 based on 25 us CCA and PUSCH
transmission in subframes N+6 to N+9 based on Category 4 LBT. The
UE succeeds with CCA LBT at subframe N+4. The UE, however, fails
with Category 4 LBT at subframe N+6, but the UE succeeds with
Category 4 LBT at subframe N+7 and continues transmission until
subframe N+9. Similar to the example in FIG. 9, the reference
subframe for the UE is subframe N+7 and the corresponding HARQ
process identifiers are H4 and H5. In the example illustrated in
FIG. 10, the UE transmission after successful LBT is detected
correctly at the eNB (i.e., H4 and H5 are decoded
successfully).
[0144] At the eNB, transport blocks corresponding to H2 and H3 are
not detected and the transport block corresponding to H6 is
detected in error. The eNB schedules all these HARQ processes
(i.e., H2, H3, and H6) with non-toggled NDI before granting the UE
with another Category 4 LBT.
[0145] For contention window adjustment, the UE looks only for NDI
of H4 and H5 and finds that they are toggled (it could also be the
case that UE wouldn't find them). Thus, the UE resets the
contention window size for the next Category 4 LBT transmission. In
the illustrated example, the UE is scheduled for Category 4 LBT at
subframe N+19. The UE resets the contention window size to its
minimum value before performing the Category 4 LBT at subframe
N+19.
[0146] As described with respect to FIGS. 9 and 10, the eNB signals
the HARQ processes with not-toggled NDI for all the failed
transmissions in the reference transmission burst. However, not all
of the not-toggled NDI contribute to the decision for contention
window adjustment. Only the not-toggled NDI corresponding to the
beginning of the transmission burst contribute. This may simplify
scheduling constraints on the eNB by enabling the eNB to only
provide the relevant information for contention window adjustment.
In particular embodiments, the following procedure is used by the
UE to increase or reset to the minimum value the contention window
size for performing LBT prior to transmission of an uplink burst
for which the eNB has indicated that LBT using a Category 4 random
backoff procedure (where contention window sizes can increase) must
be performed.
[0147] The most recently transmitted burst of contiguous subframes
that are transmitted after performing a category 4 LBT procedure
and which ended more than X ms prior to the current time is defined
as the reference transmission burst. The value of X may be chosen
such that enough time is available for providing feedback for a
transmission by the UE. For example, X=4 ms is recommended for LTE
and LAA as long as the HARQ feedback delay is at least 4 ms.
[0148] The first subframe in the reference transmission burst for
which a HARQ process identifier in that subframe has been reused
for a subsequently scheduled transmission burst is defined as the
reference subframe. After transmission of the reference subframe,
if the NDI bit for all the HARQ process identifiers in the
reference subframe are not-toggled (i.e., indicating that they are
retransmissions), the contention window size is increased to the
next higher value in the set of contention window sizes for the
priority class that was used to perform LBT prior to transmission
of the reference transmission burst. Alternatively, the contention
window size of all the LBT priority classes used by UE may be
increased to the next higher value.
[0149] Otherwise, if the NDI bit for at least one of the reference
HARQ process identifiers is toggled (i.e., indicating that the
grant is for the transmission of a new transport block or there is
no HARQ process identifier of the reference subframe), the
contention window size is reset to the minimum value in the set of
contention window sizes for the priority class that is being used
by the UE to perform LBT prior to transmission of the transmission
burst. This priority class may either be chosen by the UE based on
the traffic type it intends to transmit or may be indicated by the
eNB in the uplink grants for the current transmission burst.
Alternatively, the contention window size of all the LBT priority
classes used by the UE may be reset to the minimum value.
[0150] Particular embodiments may include the following procedure
used by the eNB. In a transmission burst received on the uplink
that was scheduled to be transmitted after a category 4 LBT
procedure by a UE, the last subframe before a subframe in which at
least one transport block was successfully received is defined as
the reference subframe. If no transport blocks in the burst were
successfully received, then the last subframe in the burst is the
reference subframe. If at least one transport block was received
successfully in each of the subframes in the burst, then there is
no reference subframe defined for the transmission burst.
[0151] If a reference subframe is defined for the transmission
burst, the eNB schedules data to the UE using all HARQ process
identifiers in the reference subframe with non-toggled
corresponding NDI at or before the time a new transmission burst is
scheduled on the uplink using a Category 4 procedure.
[0152] The HARQ process identifiers indicating retransmission need
not have been scheduled via uplink grant for a Category 4 LBT based
uplink transmission with random backoff. It could also have been
scheduled via uplink grant for a short LBT (e.g., CCA of 25 us) or
no LBT.
[0153] In the examples described above, the contention window size
is increased to the next higher value only if the NDI bit for the
reference HARQ process is not-toggled and the device actually
transmitted the reference HARQ process as the first subframe of the
prior transmission burst. This is because two types of reasons may
cause a HARQ process retransmission.
[0154] One reason is that the HARQ process was transmitted but
collision a happened. For these cases, a retransmission should use
a larger contention window size. Another reason is that the device
was not able to transmit the HARQ process in the prior scheduled
transmission burst based on the LBT protocol. That is, the device
observed occupied channel condition and refrained from transmission
to avoid collision. For these cases, the contention window size
should not be increased.
[0155] Two examples of the previous embodiments are illustrated in
FIGS. 11 and 12. From these two examples, the difference between
the embodiments described with respect to FIGS. 9 and 10 may be
better understood
[0156] FIG. 11 illustrates another example sequence of subframes
for implicitly determining an LBT contention window size, according
to some embodiments. The illustrated example includes subframes
numbered N to N+19 similar to those described with respect to FIG.
9.
[0157] The reference subframe at the UE is subframe N+7. The eNB,
however, detects that both transport blocks are detected in error
in subframe N+6 and N+7, while in subframe N+8, only one of the
transport blocks is in error. Thus, the reference subframe at the
eNB is subframe N+7. Therefore, the eNB only schedules H4 and H5
with non-toggled NDI. The reference subframe at the UE is also
subframe N+7 and the UE, for contention window adjustment, looks
for HARQ processes H4 and H5.
[0158] FIG. 12 illustrates another example sequence of subframes
for implicitly determining an LBT contention window size, according
to some embodiments. The illustrated example includes subframes
numbered N to N+19 similar to those described with respect to FIG.
10.
[0159] The reference subframe at the UE is subframe N+7. The eNB,
however, detects that both transport blocks are detected in error
in subframe N+6, while both transport blocks are detected correctly
in subframe N+7. Thus, from the eNB perspective, reference subframe
is N+6. Accordingly, the eNB schedules H2 and H3 with non-toggled
eNB.
[0160] On the other hand, the UE looks for HARQ processes H4 and H5
in its reference subframe 7 to check if they have been scheduled
and if so whether they are non-toggled or toggled (it could be that
they were not scheduled at all). Because processes H4 and H5 are
toggled, the UE resets the contention window size to minimum for
the Category 4 LBT attempt which is scheduled in subframe N+19.
[0161] Some embodiments include a correction mechanism for
contention window management. For example, some methods adjust the
contention window size by signaling the position of a reference
burst or subframe as detected at the eNB to the UE such that the UE
can use this information to compare with its actual transmission to
adjust the contention window size. In these methods, however, the
reference subframes may be signaled multiple times before the first
signaled parameter has been processed. This may happen because of
processing delays (e.g., the delay of 4 ms between the time a UE
receives a scheduling command and the time it transmits on the
uplink). Such delays can lead to the contention window size being
adjusted multiple times incorrectly. This problem can also be
caused, for example, if the UE misses an uplink grant.
[0162] To address these problems, particular embodiments may
include one or both of the following solutions. The reference
subframe may be restricted to be signaled only once (i.e., not
multiple times). In another solution, the reference subframe is
used only once by the UE for contention window size adjustment and
is ignored if it is received more than once.
[0163] General examples of the methods described above with respect
to FIGS. 9-10 are illustrated in FIG. 13 with respect to the UE,
and FIG. 14 with respect to the network node.
[0164] FIG. 13 is a flow diagram illustrating an example method in
a user equipment, according to some embodiments. In particular
embodiments, one or more steps of FIG. 13 may be performed by
components of wireless network 100 described with respect to FIG.
8.
[0165] The method begins at step 1312, where the UE transmits a
first burst of uplink subframes after a first LBT procedure. The
LBT procedure is performed using an LBT contention window size. For
example, wireless device 110 may receive burst of subframes N+6 to
N+9 illustrated in any of FIGS. 9-12.
[0166] At step 1314, the UE determines a reference subframe based
on the first burst of uplink subframes, the reference subframe
associated with a reference HARQ process identifier. In some
embodiments, determining the reference subframe comprises
determining a most recently transmitted uplink subframe in the
first burst of uplink subframes for which the associated HARQ
process identifier is also found in the received scheduling for the
second burst of uplink subframes. In some embodiments, determining
the reference subframe comprises determining the first transmitted
subframe of the first burst of uplink subframes for which the HARQ
process identifier associated with the first subframe of the first
burst of uplink subframes is also found in the received scheduling
for the second burst of uplink subframes.
[0167] For example, referring to the examples illustrated in FIGS.
9-12, wireless device 110 may determine subframe N+7 is the first
transmitted subframe of the first burst of uplink subframes.
Subframe N+6 was not transmitted because of LBT failure, thus N+7
is the first transmitted subframe.
[0168] In some examples (e.g., FIGS. 9 and 11), subframe N+7
suffered from a collision error. In other examples (e.g., FIGS. 10
and 12), subframe N+7 is received successfully by network node 120.
Either way, subframe N+7 is the first transmitted subframe (whether
successfully received or not), and is therefore determined to be
the reference subframe.
[0169] At step 1316, the UE receives scheduling for a second burst
of uplink subframes. The scheduling comprises, for each subframe of
the second burst of uplink subframes, an associated HARQ process
identifier and an associated new data indicator (NDI). For example,
wireless device 110 may receive scheduling in downlink subframe
N+11 for a second burst of subframes N+15 to N+17 illustrated in
any of FIGS. 9-12. With respect to FIG. 9, subframe N+15 is
associated with HARQ identifiers H2 and H3. The NDI for both H2 and
H3 are toggled indicating a retransmission because the previously
scheduled transmission for H2 and H3 (i.e., subframe N+6) was not
transmitted because of LBT failure. Subframe N+16 is associated
with HARQ identifiers H4 and H5. The NDI for both H4 and H5 are
toggled indicating a retransmission because the previously
transmitted subframe for H4 and H5 (e.g., subframe N+7) failed
because of a collision error. Subframe N+17 is associated with HARQ
identifiers H6 and H7. The NDI for H6 is toggled indicating a
retransmission because the previously transmitted transport block
for H6 (e.g., subframe N+8) failed because of a decoding error at
network node 120. The NDI for H7 is not-toggled indicating a new
transmission because the previously transmitted transport block for
H7 (e.g., subframe N+8) was decoded successfully at network node
120.
[0170] When the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates new data, the method continues to
step 1318 where the UE resets the LBT contention window size to a
minimum value. For example, regarding FIG. 10, wireless device 110
determined subframe N+7 is the reference subframe at previous step
1314. Subframe N+7 is associated with HARQ identifiers H4 and H5,
which were successfully received by network node 120. Thus, the NDI
associated with HARQ identifiers H4 and H5 scheduled for subframe
N+16 indicate a new transmission. Based on the indication of a new
transmission, wireless device 110 resets the Category 4 LBT
contention window size to a minimum or initial value.
[0171] When the UE determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates retransmission, the method
continues to step 1320 where the UE resets the LBT contention
window size to a minimum value. For example, regarding FIG. 9,
wireless device 110 determined subframe N+7 is the reference
subframe at previous step 1314. Subframe N+7 is associated with
HARQ identifiers H4 and H5, which were not successfully received by
network node 120. Thus, the NDI associated with HARQ identifiers H4
and H5 scheduled for subframe N+16 indicate a retransmission. Based
on the indication of a retransmission, wireless device 110
increments the Category 4 LBT contention window size.
[0172] In particular embodiments, resetting the LBT contention
window size to a minimum value comprises resetting the LBT
contention window size to a minimum value of a set of values
associated with a priority class used by the UE to perform the
first LBT procedure. For example, wireless device 110 may have used
a particular priority class for the Category 4 LBT procedure at
subframe N+7. Wireless device 110 may reset the contention window
size for that particular priority class. In some embodiments,
resetting the LBT contention window size to a minimum value may
comprise resetting LBT contention window sizes associated with all
priority classes used by the UE.
[0173] At step 1322, the UE performs a second LBT procedure using
the contention window size. For example, wireless device 110 may
use the contention window size modified at one of steps 1318 or
1320 to perform a Category 4 LBT procedure for subframe N+19 in any
of FIGS. 9-12.
[0174] Modifications, additions, or omissions may be made to method
1300. Additionally, one or more steps in method 1300 of FIG. 13 may
be performed in parallel or in any suitable order. The steps of
method 1300 may be repeated over time as necessary.
[0175] FIG. 14 is a flow diagram illustrating an example method in
a network node, according to some embodiments. In particular
embodiments, one or more steps of FIG. 14 may be performed by
components of wireless network 100 described with respect to FIG.
8.
[0176] The method begins at step 1412, where a network node
receives a first burst of uplink subframes from a wireless device
after a first LBT procedure. Each subframe of the first burst of
uplink subframes is associated with one or more transport blocks,
and each transport block is associated with a reference HARQ
process identifier. For example, with respect to FIG. 9, network
node 120 scheduled wireless device 110 to transmit uplink subframes
N+6, N+7, N+8, and N+9 after a Category 4 LBT procedure. Network
node 120 receives burst of uplink subframes N+8 and N+9 (N+6 was
not received because it was never transmitted by wireless device
110, and N+7 was not received because of a collision error).
[0177] At step 1414, the network node determines a set of transport
blocks in the first burst of uplink subframes that were not
received successfully by the network node. For example, with
respect to FIG. 9, network node 120 determines that scheduled
subframes N+6 (with transport blocks associated with HARQ process
identifiers H2 and H3) and N+7 (with transport blocks associated
with HARQ process identifiers H4 and H5) were never received.
Network node 120 also determines that the transport block
associated with HARQ identifier H6 in subframe N+8 was not decoded
successfully. Thus, the set of transport blocks in the first burst
of uplink subframes include the transport blocks associated with
HARQ identifiers H2, H3, H4, H5 and H6.
[0178] At step 1416, the network node schedules the UE with a
second burst of uplink frames using all the HARQ process
identifiers associated with the transport blocks in the determined
set of transport blocks before scheduling the UE with a second LBT
procedure. For example, with respect to FIG. 9, network node 120
schedules wireless device 110 for uplink at subframe N+15 for HARQ
processes identifiers H2 and H3, at subframe N+16 for HARQ
processes identifiers H2 and H3, and at subframe N+17 for HARQ
process identifier H6. Then network node 120 schedules the next
Category 4 LBT procedure for subframe N+19.
[0179] In some embodiments, determining the set of transport blocks
in the first burst of uplink subframes that were not received
successfully at previous step 1414 comprises determining a
reference subframe based on the last subframe before a received
subframe in which at least one transport block was received
successfully. The set of transport blocks includes the transport
blocks in the reference subframe that were not received
successfully. For example, with respect to FIG. 12, network node
120 may determine subframe N+6 is the reference subframe. N+6 is
the reference subframe because out of the burst of uplink subframes
N+6 to N+9, subframe N+7 is the first subframe in in which at least
one transport block was received successfully. The last subframe
before N+7 is N+6, thus N+6 is the reference subframe and the set
of transport blocks includes the transport blocks associated with
HARQ process identifiers H2 and H3.
[0180] In this example with respect to FIG. 12, at step 1416
network node 120 schedules wireless device 110 for uplink at
subframe N+16 for HARQ processes identifiers H2 and H3. Then
network node 120 schedules the next Category 4 LBT procedure for
subframe N+19.
[0181] Modifications, additions, or omissions may be made to method
1400. Additionally, one or more steps in method 1400 of FIG. 14 may
be performed in parallel or in any suitable order. The steps of
method 1400 may be repeated over time as necessary.
[0182] FIG. 15A is a block diagram illustrating an example
embodiment of a wireless device. The wireless device is an example
of the wireless devices 110 illustrated in FIG. 8. In particular
embodiments, the wireless device is capable of performing LBT
procedures before transmitting in the uplink.
[0183] For example, the wireless device is operable to transmit a
first burst of uplink subframes after a first LBT procedure. The
LBT procedure is performed using an LBT contention window size. The
wireless device determines a reference subframe based on the first
burst of uplink subframes. The reference subframe is associated
with a reference HARQ process identifier. The wireless device
receives scheduling for a second burst of uplink subframes. The
scheduling comprises, for each subframe of the second burst of
uplink subframes, an associated HARQ process identifier and an
associated NDI.
[0184] When the wireless device determines the HARQ process
identifier associated with at least one of the subframes of the
second burst of uplink subframes matches the reference HARQ process
identifier and the associated NDI indicates new data, the wireless
device resets the LBT contention window size to a minimum value.
When the wireless device determines the HARQ process identifier
associated with at least one of the subframes of the second burst
of uplink subframes matches the reference HARQ process identifier
and the associated NDI indicates a retransmission, the wireless
device increments the LBT contention window size. The wireless
device performs a second LBT procedure using the contention window
size.
[0185] In particular embodiments, the wireless device determines
the reference subframe by determining a most recently transmitted
uplink subframe in the first burst of uplink subframes for which
the associated HARQ process identifier is also found in the
received scheduling for the second burst of uplink subframes. In
some embodiments, the wireless device determines the reference
subframe by determining the first transmitted subframe of the first
burst of uplink subframes for which the HARQ process identifier
associated with the first subframe of the first burst of uplink
subframes is also found in the received scheduling for the second
burst of uplink subframes.
[0186] Particular examples of a wireless device include a mobile
phone, a smart phone, a PDA (Personal Digital Assistant), a
portable computer (e.g., laptop, tablet), a sensor, a modem, a
machine type (MTC) device/machine to machine (M2M) device, laptop
embedded equipment (LEE), laptop mounted equipment (LME), USB
dongles, a device-to-device capable device, a vehicle-to-vehicle
device, or any other device that can provide wireless
communication. The wireless device includes transceiver 1510,
processing circuitry 1520, memory 1530, and power source 1540. In
some embodiments, transceiver 1510 facilitates transmitting
wireless signals to and receiving wireless signals from wireless
network node 120 (e.g., via an antenna), processing circuitry 1520
executes instructions to provide some or all of the functionality
described herein as provided by the wireless device, and memory
1530 stores the instructions executed by processing circuitry 1520.
Power source 1540 supplies electrical power to one or more of the
components of wireless device 110, such as transceiver 1510,
processing circuitry 1520, and/or memory 1530.
[0187] Processing circuitry 1520 includes any suitable combination
of hardware and software implemented in one or more integrated
circuits or modules to execute instructions and manipulate data to
perform some or all of the described functions of the wireless
device. In some embodiments, processing circuitry 1520 may include,
for example, one or more computers, one more programmable logic
devices, one or more central processing units (CPUs), one or more
microprocessors, one or more applications, and/or other logic,
and/or any suitable combination of the preceding. Processing
circuitry 1520 may include analog and/or digital circuitry
configured to perform some or all of the described functions of
wireless device 110. For example, processing circuitry 1520 may
include resistors, capacitors, inductors, transistors, diodes,
and/or any other suitable circuit components.
[0188] Memory 1530 is generally operable to store computer
executable code and data. Examples of memory 1530 include computer
memory (e.g., Random Access Memory (RAM) or Read Only Memory
(ROM)), mass storage media (e.g., a hard disk), removable storage
media (e.g., a Compact Disk (CD) or a Digital Video Disk (DVD)),
and/or or any other volatile or non-volatile, non-transitory
computer-readable and/or computer-executable memory devices that
store information.
[0189] Power source 1540 is generally operable to supply electrical
power to the components of wireless device 110. Power source 1540
may include any suitable type of battery, such as lithium-ion,
lithium-air, lithium polymer, nickel cadmium, nickel metal hydride,
or any other suitable type of battery for supplying power to a
wireless device.
[0190] In particular embodiments, processing circuitry 1520 in
communication with transceiver 1510 performs LBT procedures before
transmitting in the uplink. For example, processing circuitry 1520
in communication with transceiver 1510 receives scheduling for a
current burst of contiguous uplink subframes, determine a reference
subframe based on a previously-scheduled burst of contiguous uplink
subframes, and adjusts an LBT contention window based on the
reference subframe.
[0191] Other embodiments of the wireless device may include
additional components (beyond those shown in FIG. 15A) responsible
for providing certain aspects of the wireless device's
functionality, including any of the functionality described above
and/or any additional functionality (including any functionality
necessary to support the solution described above).
[0192] FIG. 15B is a block diagram illustrating example components
of a wireless device 110. The components may include transmitting
module 1550, determining module 1552, LBT module 1554, and
receiving module 1556.
[0193] Transmitting module 1550 may perform the transmitting
functions of wireless device 110. For example, transmitting module
1550 may transmit a first burst of uplink subframes after a first
LBT procedure. Transmitting module 1550 may perform the
transmitting functions described in any of the examples above,
including FIGS. 9-14. In certain embodiments, transmitting module
1550 may include or be included in processing circuitry 1520. In
particular embodiments, transmitting module 1550 may communicate
with determining module 1552, LBT module 1554, and receiving module
1556.
[0194] Determining module 1552 may perform the determining
functions of wireless device 110. For example, determining module
1552 may determine a reference subframe and determine a contention
window size as described in any of the examples above, including
FIGS. 9-14. In certain embodiments, determining module 1552 may
include or be included in processing circuitry 1520. In particular
embodiments, determining module 1552 may communicate with
transmitting module 1550, LBT module 1554, and receiving module
1556.
[0195] LBT module 1554 may perform the listen-before-talk functions
of wireless device 110. For example, LBT module 1554 may perform an
LBT procedure with random backoff or perform a fixed duration clear
channel assessment. LBT module 1554 may increment or rest a
contention window size for performing LBT. In certain embodiments,
LBT module 1554 may include or be included in processing circuitry
1520. In particular embodiments, LBT module 1554 may communicate
with transmitting module 1550, determining module 1552, and
receiving module 1556.
[0196] Receiving module 1556 may perform the receiving functions of
wireless device 110. For example, receiving module 1556 may receive
scheduling for a burst of uplink subframes. In certain embodiments,
receiving module 1556 may include or be included in processing
circuitry 1520. In particular embodiments, receiving module 1556
may communicate with transmitting module 1550, determining module
1552 and LBT module 1554.
[0197] FIG. 16A is a block diagram illustrating an example
embodiment of a network node. The network node is an example of the
network node 120 illustrated in FIG. 8. In particular embodiments,
the network node is capable of managing contention window sizes and
signaling the contention window size to a wireless device. For
example, the network node may receive a first burst of uplink
subframes from a wireless device after a first LBT procedure. Each
subframe of the first burst of uplink subframes is associated with
one or more transport blocks, and each transport block is
associated with a HARQ process identifier. The network node
determines a set of transport blocks in the first burst of uplink
subframes that were not received successfully by the network node.
Before scheduling the wireless device with a second LBT procedure,
the network node schedules the wireless device with a second burst
of uplink frames using all the HARQ process identifiers associated
with the transport blocks in the determined set of transport
blocks.
[0198] In particular embodiments, the network node determines a
reference subframe based on the last subframe before a received
subframe in which at least one transport block was received
successfully. The set of transport blocks includes the transport
blocks in the reference subframe that were not received
successfully.
[0199] Network node 120 can be an eNodeB, a nodeB, a base station,
a wireless access point (e.g., a Wi-Fi access point), a low power
node, a base transceiver station (BTS), a transmission point or
node, a remote RF unit (RRU), a remote radio head (RRH), or other
radio access node. The network node includes at least one
transceiver 1610, at least one processing circuitry 1620, at least
one memory 1630, and at least one network interface 1640.
Transceiver 1610 facilitates transmitting wireless signals to and
receiving wireless signals from a wireless device, such as wireless
devices 110 (e.g., via an antenna); processing circuitry 1620
executes instructions to provide some or all of the functionality
described above as being provided by a network node 120; memory
1630 stores the instructions executed by processing circuitry 1620;
and network interface 1640 communicates signals to backend network
components, such as a gateway, switch, router, Internet, Public
Switched Telephone Network (PSTN), controller, and/or other network
nodes 120. Processing circuitry 1620 and memory 1630 can be of the
same types as described with respect to processing circuitry 1520
and memory 1530 of FIG. 15A above.
[0200] In some embodiments, network interface 1640 is
communicatively coupled to processing circuitry 1620 and refers to
any suitable device operable to receive input for network node 120,
send output from network node 120, perform suitable processing of
the input or output or both, communicate to other devices, or any
combination of the preceding. Network interface 1640 includes
appropriate hardware (e.g., port, modem, network interface card,
etc.) and software, including protocol conversion and data
processing capabilities, to communicate through a network.
[0201] In particular embodiments, processing circuitry 1620 in
communication with transceiver 1610 determines a reference subframe
for signaling information about contention window sizes.
[0202] Other embodiments of network node 120 include additional
components (beyond those shown in FIG. 16A) responsible for
providing certain aspects of the network node's functionality,
including any of the functionality described above and/or any
additional functionality (including any functionality necessary to
support the solution described above). The various different types
of network nodes may include components having the same physical
hardware but configured (e.g., via programming) to support
different radio access technologies, or may represent partly or
entirely different physical components.
[0203] FIG. 16B is a block diagram illustrating example components
of a network node 120. The components may include receiving module
1650, determining module 1652 and LBT module 1654.
[0204] Receiving module 1650 may perform the receiving functions of
network node 120. For example, receiving module 1650 may receive a
burst of uplink subframes from a wireless device after an LBT
procedure. In certain embodiments, receiving module 1650 may
include or be included in processing circuitry 1620. In particular
embodiments, receiving module 1650 may communicate with determining
module 1652 and LBT module 1654.
[0205] Determining module 1652 may perform the determining
functions of network node 120. For example, determining module 1652
may determine a set of transport blocks in the burst of uplink
subframes that were not received successfully by the network node.
In certain embodiments, determining module 1652 may include or be
included in processing circuitry 1620. In particular embodiments,
determining module 1652 may communicate with receiving module 1650
and LBT module 1654.
[0206] LBT module 1654 may perform the LBT functions of network
node 120. For example, LBT module 1654 may schedule the wireless
device with a second burst of uplink frames using all the HARQ
process identifiers associated with the unsuccessfully received
transport blocks. In certain embodiments, LBT module 1654 may
include or be included in processing circuitry 1620. In particular
embodiments, LBT module 1654 may communicate with receiving module
1650 and determining module 1652.
[0207] Modifications, additions, or omissions may be made to the
systems and apparatuses disclosed herein without departing from the
scope of the invention. The components of the systems and
apparatuses may be integrated or separated. Moreover, the
operations of the systems and apparatuses may be performed by more,
fewer, or other components. Additionally, operations of the systems
and apparatuses may be performed using any suitable logic
comprising software, hardware, and/or other logic. As used in this
document, "each" refers to each member of a set or each member of a
subset of a set.
[0208] Modifications, additions, or omissions may be made to the
methods disclosed herein without departing from the scope of the
invention. The methods may include more, fewer, or other steps.
Additionally, steps may be performed in any suitable order.
[0209] Although this disclosure has been described in terms of
certain embodiments, alterations and permutations of the
embodiments will be apparent to those skilled in the art.
Accordingly, the above description of the embodiments does not
constrain this disclosure. Other changes, substitutions, and
alterations are possible without departing from the spirit and
scope of this disclosure, as defined by the claims below.
[0210] Abbreviations used in the preceding description include:
[0211] 3GPP Third Generation Partnership Project
[0212] ACK Acknowledgement
[0213] BTS Base Transceiver Station
[0214] CCA Clear Channel Assessment
[0215] CW Contention Window
[0216] D2D Device to Device
[0217] DCF Distributed Coordination Function
[0218] DIFS DCF Inter-Frame Spacing
[0219] DL Downlink
[0220] eNB eNodeB
[0221] FDD Frequency Division Duplex
[0222] HARQ Hybrid Automatic Repeat Request
[0223] LAA License Assisted Access
[0224] LBT Listen-Before-Talk
[0225] LTE Long Term Evolution
[0226] MAC Medium Access Control
[0227] M2M Machine to Machine
[0228] MIMO Multi-Input Multi-Output
[0229] MRBC Multiple Random Backoff Channels
[0230] MTC Machine Type Communication
[0231] NAK Negative Acknowledgement
[0232] NR New Radio
[0233] PDSCH Physical Downlink Shared Channel
[0234] PIFS PCF Inter-Frame Spacing
[0235] PUCCH Physical Uplink Control Channel
[0236] QCI QoS Class Indicator
[0237] QoS Quality of Service
[0238] RAN Radio Access Network
[0239] RAT Radio Access Technology
[0240] RB Radio Bearer
[0241] RBS Radio Base Station
[0242] RNC Radio Network Controller
[0243] RRC Radio Resource Control
[0244] RRH Remote Radio Head
[0245] RRU Remote Radio Unit
[0246] SCell Secondary Cell
[0247] SRBC Single Random Backoff Channel
[0248] SIFS Short Inter-Frame Spacing
[0249] TDD Time Division Duplex
[0250] UE User Equipment
[0251] UL Uplink
[0252] UTRAN Universal Terrestrial Radio Access Network
[0253] WAN Wireless Access Network
* * * * *