U.S. patent application number 14/111456 was filed with the patent office on 2014-01-30 for method and apparatus for user equipment in battery saving mode transmitting reverse direction control signal in mobile communication system.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. The applicant listed for this patent is Kyeong In Jeong, Soeng Hun Kim, Gert-Jan Van Lieshout. Invention is credited to Kyeong In Jeong, Soeng Hun Kim, Gert-Jan Van Lieshout.
Application Number | 20140029563 14/111456 |
Document ID | / |
Family ID | 47284463 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140029563 |
Kind Code |
A1 |
Kim; Soeng Hun ; et
al. |
January 30, 2014 |
METHOD AND APPARATUS FOR USER EQUIPMENT IN BATTERY SAVING MODE
TRANSMITTING REVERSE DIRECTION CONTROL SIGNAL IN MOBILE
COMMUNICATION SYSTEM
Abstract
The present disclosure relates to a method and apparatus for a
user equipment to transmit control signals to a base station in a
wireless communication system supporting discontinuous reception
(DRX). In particular, the method for a user equipment to transmit
control signals to a base station includes: receiving a downlink
control channel indicating new uplink or downlink transmission in a
first period preset with reference to the last subframe of an
active time; and selectively skipping transmission of a control
signal in a preset second period starting from a subframe at which
the downlink control channel is received. In addition, a user
equipment transmitting control signals to a base station includes:
a transceiver unit to send and receive signals to and from the base
station; and a control unit determining, when a downlink control
channel indicating new uplink or downlink transmission is received
by the transceiver unit in a first period preset with reference to
the last subframe of an active time, whether to selectively
transmit a control signal in a preset second period starting from a
subframe at which the downlink control channel is received.
Inventors: |
Kim; Soeng Hun;
(Gyeonggi-do, KR) ; Van Lieshout; Gert-Jan;
(Middlesex, GB) ; Jeong; Kyeong In; (Gyeonggi-do,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Soeng Hun
Van Lieshout; Gert-Jan
Jeong; Kyeong In |
Gyeonggi-do
Middlesex
Gyeonggi-do |
|
KR
GB
KR |
|
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Gyeonggi-do
KR
|
Family ID: |
47284463 |
Appl. No.: |
14/111456 |
Filed: |
April 10, 2012 |
PCT Filed: |
April 10, 2012 |
PCT NO: |
PCT/KR2012/002727 |
371 Date: |
October 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61473966 |
Apr 11, 2011 |
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61521910 |
Aug 10, 2011 |
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61531185 |
Sep 6, 2011 |
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61552114 |
Oct 27, 2011 |
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61553359 |
Oct 31, 2011 |
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61556779 |
Nov 7, 2011 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 12/10 20130101;
H04W 12/02 20130101; H04W 28/06 20130101; H04W 48/20 20130101; H04W
84/045 20130101; H04W 92/00 20130101; H04W 12/0017 20190101; H04W
76/27 20180201; H04W 72/10 20130101; H04W 36/04 20130101; H04W
52/0216 20130101; H04W 74/08 20130101; H04W 40/02 20130101; H04W
52/0254 20130101; H04W 36/0083 20130101; Y02D 30/70 20200801; H04W
76/28 20180201 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 76/04 20060101
H04W076/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2012 |
KR |
10-2012-0037390 |
Claims
1. A method for a user equipment to transmit control signals to a
base station in a wireless communication system supporting
discontinuous reception (DRX), the method comprising: receiving a
downlink control channel indicating new uplink or downlink
transmission in a first period preset with reference to the last
subframe of an active time; and selectively skipping transmission
of a control signal in a preset second period starting from a
subframe at which the downlink control channel is received.
2. The method of claim 1, wherein the selectively skipping of the
transmission is not applied at a duration starting from the
subframe at which the downlink control channel is received and
ending at the last subframe of the active time within the second
period.
3. The method of claim 2, wherein the first period is a duration
consisting of the last subframe of the active time and i subframes
preceding the last subframe (i: an integer ranging from 0 to 3
inclusive).
4. The method of claim 3, wherein the second period is a duration
consisting of the subframe at which the downlink control channel is
received and subsequent three subframes thereof.
5. The method of claim 4, wherein the selectively skipping of the
transmission further comprises transmitting the control signal at a
duration starting from the subframe at which the downlink control
channel is received and ending at the last subframe of the active
time within the second period.
6. The method of claim 5, wherein the control signal is at least
one of an uplink control channel signal including CQI/PMI/RI/PTI or
a sounding reference signal.
7. A user equipment transmitting control signals to a base station
in a wireless communication system supporting discontinuous
reception (DRX), the user equipment comprising: a transceiver unit
to send and receive signals to and from the base station; and a
control unit determining, when a downlink control channel
indicating new uplink or downlink transmission is received by the
transceiver unit in a first period preset with reference to the
last subframe of an active time, whether to selectively transmit a
control signal in a preset second period starting from a subframe
at which the downlink control channel is received.
8. The user equipment of claim 7, wherein the control unit does not
determine whether to selectively transmit a control signal at a
duration starting from the subframe at which the downlink control
channel is received and ending at the last subframe of the active
time within the second period.
9. The user equipment of claim 8, wherein the first period is a
duration consisting of the last subframe of the active time and i
subframes preceding the last subframe (i: an integer ranging from 0
to 3 inclusive).
10. The user equipment of claim 9, wherein the second period is a
duration consisting of the subframe at which the downlink control
channel is received and subsequent three subframes thereof.
11. The user equipment of claim 10, wherein the control unit
controls an operation to transmit the control signal at a duration
starting from the subframe at which the downlink control channel is
received and ending at the last subframe of the active time within
the second period.
12. The user equipment of claim 11, wherein the control signal is
at least one of an uplink control channel signal including
CQI/PMI/RI/PTI or a sounding reference signal.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method and apparatus for
transmitting uplink control signals for a user equipment in
discontinuous reception (DRX) operation in a mobile communication
system.
BACKGROUND ART
[0002] In general, mobile communication systems have been developed
to provide communication services while guaranteeing user mobility.
Thanks to rapid technological advancement, mobile communication
systems are capable of providing not only voice communication
services but also high-speed data communication services.
[0003] Recently, the 3rd Generation Partnership Project (3GPP) has
been working to standardize specifications for the Long Term
Evolution (LTE) system as a next generation mobile communication
system. The LTE system is expected to be commercially available in
about 2010, and aims to realize high-speed packet based
communication supporting a data rate of 100 Mbps exceeding existing
data rates. With completion of LTE system standardization, to
achieve higher data rates, 3GPP started to develop the LTE-Advanced
(LTE-A) system by introducing various new communication schemes to
the LTE system. In the description, the existing LTE system and the
LTE-A system are collectively referred to as the LTE system.
[0004] Carrier aggregation (CA) and MIMO are representative ones of
the communication schemes to be newly introduced. Carrier
aggregation is a technology that enables a user equipment to send
and receive data using multiple carriers. Here, the user equipment
may send and receive data through a number of cells (normally,
these cells belong to the same base station) associated with
multiple aggregated carriers.
DISCLOSURE OF INVENTION
Technical Problem
[0005] An aspect of the present disclosure is to provide a method
and apparatus that enable a user equipment supporting discontinuous
reception (DRX) to distinguish a subframe in which control signal
transmission is mandatory from another subframe in which control
signal transmission is optional when the active time is
extended.
Solution to Problem
[0006] In accordance with an aspect of the present disclosure, a
method for a user equipment to transmit control signals to a base
station in a wireless communication system supporting discontinuous
reception (DRX) is provided. The method may include: receiving a
downlink control channel indicating new uplink or downlink
transmission in a first period preset with reference to the last
subframe of an active time; and selectively skipping transmission
of a control signal in a preset second period starting from a
subframe at which the downlink control channel is received.
[0007] In accordance with another aspect of the present disclosure,
a user equipment transmitting control signals to a base station in
a wireless communication system supporting discontinuous reception
(DRX)is provided. The user equipment may include: a transceiver
unit to send and receive signals to and from the base station; and
a control unit determining, when a downlink control channel
indicating new uplink or downlink transmission is received by the
transceiver unit in a first period preset with reference to the
last subframe of an active time, whether to selectively transmit a
control signal in a preset second period starting from a subframe
at which the downlink control channel is received.
Advantageous Effects of Invention
[0008] In a feature of the present disclosure, for transmission of
uplink control signals in a mobile communication system, a user
equipment in DRX operation is capable of distinguishing a situation
where higher than normal processing power maybe needed from another
situation where higher than normal processing power is not needed
and is allowed to send an uplink control signal only when higher
than normal processing power is not needed. Hence, it is possible
to prevent loss of uplink control signals.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 illustrates an LTE system architecture, to which the
present disclosure is applied.
[0010] FIG. 2 illustrates a hierarchy of wireless protocols in the
LTE system, to which the present disclosure is applied.
[0011] FIG. 3 illustrates carrier aggregation supported by a user
equipment.
[0012] FIG. 4 depicts a first embodiment of the present
disclosure.
[0013] FIG. 5 is a sequence diagram describing UE and ENB
operations according to the first embodiment of the present
disclosure.
[0014] FIG. 6 is a flowchart describing UE operation according to
the first embodiment of the present disclosure.
[0015] FIG. 7 is a sequence diagram describing UE and ENB
operations according to a second embodiment of the present
disclosure.
[0016] FIG. 8 is a flowchart describing UE operation according to
the second embodiment of the present disclosure.
[0017] FIG. 9 is a flowchart describing UE operation according to a
third embodiment of the present disclosure.
[0018] FIG. 10 is a block diagram of a user equipment according to
an embodiment of the present disclosure.
[0019] FIG. 11 is a block diagram of a base station according to an
embodiment of the present disclosure.
MODE FOR THE INVENTION
[0020] Hereinafter, embodiments of the present disclosure are
described in detail with reference to the accompanying drawings.
Detailed descriptions of well-known functions and structures
incorporated herein may be omitted to avoid obscuring the subject
matter of the present disclosure.
[0021] The present disclosure relates to a method and apparatus
used by a user equipment to report performance thereof to the
network. Before description of the present disclosure, the LTE
system and carrier aggregation are described in brief.
[0022] FIG. 1 illustrates an LTE system architecture, to which the
present disclosure is applied.
[0023] Referring to FIG. 1, an LTE radio access network is composed
of base stations (Evolved Node B, Node B, or ENB) 105, 110, 115 and
120, a Mobility Management Entity (MME) 125, and a Serving-Gateway
(S-GW) 130. A User Equipment (UE) 135 may connect to an external
network through the ENBs 105 to 120 and the S-GW 130.
[0024] In FIG. 1, the ENBs 105 to 120 correspond to Node Bs of the
existing UMTS system. The ENB is connected to the UE 135 through a
radio channel, and may perform more complex functions in comparison
to the existing Node B. In the LTE system, as all user traffic
including real-time services like VoIP (Voice over IP) services is
served by shared channels, an entity is needed to perform
scheduling on the basis of status information collected from UEs
such as information on buffer states, available transmit power and
channels. Each of the ENBs 105 to 120 performs this scheduling
function.
[0025] In most cases, a single ENB controls multiple cells. To
achieve a data rate of 100 Mbps, the LTE system utilizes Orthogonal
Frequency Division Multiplexing (OFDM) in, for example, a 20 MHz
bandwidth as radio access technology. Adaptive modulation and
coding (AMC) is employed to determine the modulation scheme and
channel coding rate according to UE channel states. The S-GW 130
provides data bearers, and creates and removes a data bearer under
control of the MME 125. The MME 125 performs various control
functions including UE mobility management and is connected to
multiple ENBs.
[0026] FIG. 2 illustrates a hierarchy of wireless protocols in the
LTE system, to which the present disclosure is applied.
[0027] Referring to FIG. 2, for a UE and ENB in the LTE system, the
wireless protocol stack is composed of Packet Data Convergence
Protocol (PDCP) 205 or 240, Radio Link Control (RLC) 210 or 235,
Medium Access Control (MAC) 215 or 230, and a physical (PHY) layer
220 or 225. The PDCP 205 or 240 performs compression and
decompression of IP headers. The RLC 210 or 235 reconfigures PDCP
PDUs (Protocol Data Unit) to a suitable size to conduct ARQ
operations and the like.
[0028] The MAC 215 or 230 is connected to multiple RLC layer units
in the same UE, and multiplexes RLC PDUs into MAC PDUs or
demultiplexes MAC PDUs into RLC PDUs. The physical layer 220 or 225
converts higher layer data into OFDM symbols by means of channel
coding and modulation and transmits the OFDM symbols through a
wireless channel, or converts OFDM symbols received through a
wireless channel into higher layer data by means of demodulation
and channel decoding and forwards the data to higher layers.
[0029] FIG. 3 illustrates carrier aggregation supported by a user
equipment.
[0030] Referring to FIG. 3, one ENB transmits and receives multiple
carriers across multiple frequency bands. For example, assume that
the ENB 305 transmits a carrier 315 with a center frequency f1 and
a carrier 310 with a center frequency f3. An existing UE may use
one of the two carriers to send and receive data. However, a UE
having a carrier aggregation capability may send and receive data
to and from multiple carriers in parallel. Here, the ENB 305 may
assign more carriers to the UE 330 having a carrier aggregation
capability according to situations, increasing the data rate of the
UE 330.
[0031] In a traditional sense, it may be considered that one cell
is formed by a downlink carrier and an uplink carrier provided by
the same base station. In carrier aggregation, a user equipment may
be considered as sending and receiving data through multiple cells
in parallel. Hence, the maximum data rate of the user equipment may
be increased in proportion to the number of aggregated
carriers.
[0032] In the following description, for a UE, data reception
through a downlink carrier and data transmission through an uplink
carrier may be identical in meaning to data transmission and
reception through control and data channels provided by cells
corresponding to center frequencies and frequency bands
characterizing the above carriers.
[0033] For efficient utilization of radio transmission resources in
a given communication network, the UE sends preset control
information to the ENB on a regular or occasional basis. For
example, such control information may include Channel Quality
Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indicator
(RI), Precoding Type Indicator (PTI), Sounding Reference Signal
(SRS), and HARQ feedback signal. Here, CQI, PMI, RI and PTI may
also be referred to as Channel State Information (CSI). The CSI
maybe transmitted through Physical Uplink Control Channel (PUCCH)
or be embedded in a part of Physical Uplink Shared Channel (PUSCH)
for transmission. The SRS may be transmitted at the last symbol of
the PUSCH.
[0034] These information may be information on downlink channel
quality experienced by the UE, information usable by the ENB to
estimate uplink channel quality experienced by the UE, or HARQ
feedback information as to downlink data. Uplink control signals
excluding the SRS are transmitted only by the Primary Cell (PCell),
and the SRS may also be transmitted by a Secondary Cell (SCell). As
described before, when carrier aggregation is used, multiple
serving cells maybe assigned to one UE, and one thereof is the
PCell and the others are SCells. The PCell and SCell may be defined
as follows.
[0035] Primary Cell: the cell, operating on the primary frequency,
in which the UE either performs the initial connection
establishment procedure or initiates the connection
re-establishment procedure, or the cell indicated as the primary
cell in the handover procedure.
[0036] Secondary Cell: a cell, operating on a secondary frequency,
which may be configured once an RRC connection is established and
which may be used to provide additional radio resources.
[0037] To minimize battery power consumption, a UE may operate in
discontinuous reception (DRX) mode. Section 5.7 of 3GPP TS 36.321
may be referred for DRX related information. During DRX mode, a UE
may monitor the Physical Downlink Control Channel (PDCCH) only for
a particular duration set as the active time, so that the UE may
switch off the transceiver thereof for the other duration. For ease
of description, some DRX-related terms are described below.
[0038] Active Time: a time duration in which PDCCH reception is
required during DRX operation. The active time may include the time
while: [0039] onDurationTimer or drx-InactivityTimer or
drx-RetransmissionTimer or mac-ContentionResolutionTimer is running
(first type active time); or [0040] a Scheduling Request is sent on
PUCCH and is pending (second type active time); or [0041] an uplink
grant for a pending HARQ retransmission can occur and there is data
in the corresponding HARQ buffer (third type active time); or
[0042] a PDCCH indicating a new transmission addressed to the
C-RNTI of the UE has not been received after successful reception
of a Random Access Response for the preamble not selected by the UE
(fourth type active time).
[0043] A UE in DRX mode sends the CSI and SRS in the active time
and does not send the same in the non-active time. In normal
situations, such DRX mode operation does not cause a problem.
[0044] However, when the active time is unexpectedly extended,
owing to failure of preparation for sending an uplink control
signal, the UE may be unable to transmit such uplink control signal
in a section of the active time. This problem may occur
particularly when the CSI signal is to be multiplexed on the PUSCH
for transmission.
[0045] For example, assume that a UE is scheduled to perform PUSCH
transmission at the subframe n+m and the active time is extended
due to reception of a new scheduling request at the subframe n+m-k.
Before the subframe n+m-k, the UE may prepare PUSCH transmission
without CSI multiplexed at the subframe n+m. Owing to unexpected
extension of the active time at subframe n+m-k, the UE has to
change transmission at the subframe n+m to PUSCH transmission with
CSI multiplexed. However, the UE may be unable to make such a
sudden change, and hence may have to prepare both PUSCH
transmission without CSI multiplexed and PUSCH transmission with
CSI multiplexed.
[0046] In the present disclosure, to address the above problem,
when the active time is unexpectedly extended, a duration in which
the CSI has to be transmitted is separated from a duration in which
CSI transmission is determined according to UE capabilities.
First Embodiment
[0047] FIG. 4 depicts the first embodiment of the present
disclosure.
[0048] With reference to a subframe 405 at which the active time is
expected to end according to expiration of onDurationTimer or
drx-inactivityTimer, a first period, second period, third period
and fourth period are defined. In the following description, it is
assumed that the subframe n is a subframe at which the active time
is expected to end and the subframe n-k is a subframe at which an
event extending the active time has occurred.
[0049] First period: a duration consisting of the subframe n and
m-1 subframes preceding the subframe n. If m is assumed to be 4,
the subframe n-3, subframe n-2, subframe n-1 and subframe n
constitute the first period. In the present disclosure, when the
active time is extended in the first period, the UE regards this
extension as unexpected and may behave differently from the case of
other active time extensions.
[0050] Here, m is a parameter related to processing capabilities to
cope with active time extension. It is preferable for m to have a
single fixed value for all UEs including low end terminals with low
performance.
[0051] Second period: a duration consisting of a subframe at which
an event extending the active time (e.g. PDCCH reception indicating
new transmission) has occurred and m-1 subframes following the
subframe. For example, if an event extending the active time has
occurred at a subframe n-3 and m is 4, the second period consists
of the subframe n-3, subframe n-2, subframe n-1 and subframe n. If
an event extending the active time has occurred at a subframe n-2,
the second period consists of the subframe n-2, subframe n-1,
subframe n and subframe n+1.
[0052] Third period: a duration in which the first period and
second period overlap each other. That is, the third period
consists of the subframes [n-k, n] (from n-k to n, inclusive). The
last subframe of the third period is the subframe at which the
active time has been expected to end.
[0053] As the third period has already belonged to the active time
before extension of the active time, it is possible to transmit the
CSI and SRS regardless of UE processing capabilities. Hence,
determination of whether to transmit the CSI and SRS by the UE may
reduce the chance for the ENB to receive the CSI and SRS, causing
system performance degradation.
[0054] Fourth period: a duration of the second period not
overlapping with the first period. That is, the fourth period
consists of the subframes [n+1, n-k+m] (inclusive). The UE may be
able or unable to transmit the CSI and SRS during the fourth period
according to UE capability and the fourth period length.
[0055] For example, as the fourth period length approaches to m
(that is, as the occurrence time of an event extending the active
time becomes closer to the last subframe of the active time), the
possibility of CSI and SRS transmission becomes lower in the former
part of the fourth period and becomes higher in the latter part
thereof. CSI and SRS transmission is possible after the fourth
period.
[0056] When the active time is extended in the first period, the UE
identifies the second, third and fourth periods. In subframes of
the third period, the UE transmits the CSI and SRS (if CSI and SRS
transmission is scheduled in these subframes). In subframes of the
fourth period, the UE transmits the CSI and SRS if possible or does
not transmit the CSI and SRS if not possible. After the fourth
period, the UE normally transmits the CSI and SRS.
[0057] In other words, assuming that k is an integer between 0 and
m-1, when the active time is extended according to reception of UL
grant or DL assignment indicating new transmission at the subframe
n-k, the UE normally transmits the CSI and SRS in subframes[n-k, n]
corresponding to the third period, may skip CSI and SRS
transmission in subframes[n+1, n+m-k] corresponding to the fourth
period, and normally transmits the CSI and SRS after the subframe
n+m-k.
[0058] In the present disclosure, as the UE clearly specifies a
duration in which the CSI and SRS are to be transmitted, the
frequency for the ENB to receive valid CSI and SRS information is
increased, leading to system performance enhancement.
[0059] FIG. 5 describes UE and ENB operations according to the
first embodiment of the present disclosure.
[0060] At operation 505, the UE receives various configuration
information (described below) from the ENB and performs DRX,
CSI/SRS configuration and the like. [0061] DRX configuration
information: onDurationTimer, drx-InactivityTimer,
drx-RetransmissionTimer, longDRX-CycleStartOffset,
drxShortCycleTimer and the like [0062] PUCCH configuration
information: information related to CSI transmission such as
transmission resources and cycles to use for CSI transmission
[0063] PUSCH/PUCCH parallel transmission configuration information:
a UE may perform PUSCH transmission and PUCCH transmission in
parallel according to its capabilities. As such UE may separately
perform CSI transmission and PUSCH transmission without
multiplexing, it may be free from or less seriously affected by the
above described problem. The ENB may configure PUSCH/PUCCH parallel
transmission for a specific UE in consideration of reported UE
capability information and cell conditions.
[0064] At operation 510, the UE starts DRX operation. This
indicates that the UE repeats a cycle of active time and non-active
time according to preset rules and conditions. The UE monitors the
PDCCH and transmits the CSI and SRS on the PUCCH during the active
time, and does not monitor the PDCCH and does not transmit the CSI
and SRS on the PUCCH during non-active time.
[0065] Here, CSI transmission on PUCCH (CSI on PUCCH) indicates
that CSI information is transmitted through PUCCH transmission
resources. CSI information is normally transmitted through PUCCH
transmission resources, but may be transmitted through PUSCH
transmission resources (CSI on PUSCH) in some exceptional
cases.
[0066] The following is examples of CSI on PUCCH. [0067] CSI is
transmitted alone in PUCCH [0068] CSI is transmitted with HARQ
feedback in PUCCH [0069] CSI is transmitted with SR in PUCCH
[0070] When the CSI is transmitted together with a different
control signal, the transport format for the CSI is changed to a
pre-agreed transport format capable of sending the CSI together
with the different control signal. Scheduling Request (SR) is a
1-bit signal sent by the UE to the ENB as a request for
transmission resource allocation.
[0071] The following is examples of CSI on PUSCH. [0072] CSI is
transmitted together with PUSCH when PUSCH is scheduled in the
subframe where periodic CSI is configured [0073] CSI is transmitted
together with PUSCH when a periodic CSI is requested upon receiving
PDCCH whose CQI-request bit is set
[0074] As CSI transmission through the PUSCH is predictable, the
format change problem does not arise. Hence, during the fourth
period, the UE is given freedom as to CSI transmission only in the
case of CSI on PUCCH and is forced to transmit the CSI in the case
of CSI on PUSCH.
[0075] At operation 515, the active time is unexpectedly extended.
For example, assuming that the active time is scheduled to end at a
subframe owing to expiration of onDurationTimer or
drx-inactivityTimer, when a PDCCH indicating new downlink
transmission or uplink transmission resource allocation is received
within the first period set with reference to the subframe, the
active time may be extended.
[0076] At operation 520, the UE determines the second period, third
period and fourth period.
[0077] Thereafter, the UE performs operations in accordance with
the determined periods. More specifically, the UE performs CSI on
PUCCH, CSI on PUSCH, and SRS transmission during the third period.
The SRS may be configured not only on the PCell but also on the
SCell. During the third period, the UE performs SRS transmission in
all serving cells where the SRS is configured and SRS transmission
is scheduled in the third period.
[0078] During the fourth period, the UE may skip CSI on PUCCH and
SRS transmission for the PCell and may perform CSI on PUSCH and SRS
transmission for the SCell. Alternatively, the UE may perform CSI
on PUCCH and SRS transmission for the PCell on a best effort basis
during the fourth period.
[0079] That is, if time enough to prepare uplink transmission is
given between a subframe at which an uplink control signal request
is received and a subframe at which uplink transmission is to be
performed, the UE performs CSI on PUCCH and SRS transmission for
the PCell. Otherwise, the UE skips CSI on PUCCH and SRS
transmission for the PCell. After the fourth period, the UE
performs CSI on PUCCH and SRS transmission for each serving
cell.
[0080] FIG. 6 is a flowchart describing UE operation according to
the first embodiment of the present disclosure.
[0081] At operation 605, the UE receives various configuration
information from the ENB and performs DRX, CSI and SRS
configuration accordingly.
[0082] At operation 610, the UE initiates DRX operation and CSI/SRS
transmission.
[0083] When the active time is extended at operation 615, the UE
proceeds to operation 620 at which the UE checks whether the active
time extension is expected or unexpected. Here, unexpected
extension refers to generation of an event extending the active
time within a preset duration preceding the last subframe of the
active time. Expected extension refers to generation of an event
extending the active time before the preset duration preceding the
last subframe of the active time.
[0084] If the extension is expected, the UE proceeds to operation
625 at which the UE continues CSI/SRS transmission in the active
time. If the extension is unexpected, the UE proceeds to operation
630 at which the UE checks whether PUSCH/PUCCH parallel
transmission is configured.
[0085] If PUSCH/PUCCH parallel transmission is configured, as a
transport format change is not a serious problem, the UE proceeds
to operation 625.
[0086] If PUSCH/PUCCH parallel transmission is not configured, the
UE proceeds to operation 635 at which the UE determines the third
period and fourth period. At operation 640, the UE performs
operations in accordance with each period. After the fourth period,
the UE returns to operation 625 and continues CSI/SRS transmission
during the active time.
[0087] The ENB receiving CSI/SRS information, as in the case of the
UE, may determine the third period and fourth period and consider
that the UE performs CSI/SRS transmission after the third period
and the fourth period, the UE may or may not perform CSI/SRS
transmission during the fourth period, and, when the third period
is short in particular, occurrence of CSI/SRS transmission is
highly improbable in the former part of the fourth period.
[0088] Here, the sum of the third period length and the fourth
period length is always the same, and the third period length and
the fourth period length may each be varied according to the point
in time when an event extending the active time occurs.
Second Embodiment
[0089] The SRS is used by the ENB to identify UE uplink channel
states and to maintain UE uplink transmission timing. For
identifying uplink channel states, it is preferable to steadily
transmit the SRS with a long cycle; and, for maintaining uplink
transmission timing, it is preferable to frequently transmit the
SRS with a short cycle at a point in time when uplink data
transmission is expected.
[0090] To address these conflicts, the present disclosure uses two
types of SRS: long term SRS (or RRC-SRS) and short term SRS (or
L1-SRS).
[0091] Long term SRS: it is configured and enabled by an RRC
control message. SRS transmission resources and cycles are
configured by the RRC control message. The UE periodically
transmits the long term SRS if a preset condition is satisfied. As
the long term SRS is enabled by an RRC control message, it cannot
be rapidly enabled or disabled but may provide more detailed
configuration information.
[0092] Short term SRS: it is configured and enabled through the
PDCCH. Information regarding SRS transmission resources, cycles and
repetition count are configured through PDCCH. When such a PDCCH is
received, the UE performs SRS transmission. Some of the
configuration information such as the cycle and repetition count
may be configured in advance through an RRC control message. As the
short term SRS is enabled through L1 signaling, it may be rapidly
enabled in comparison to the RRC-SRS.
[0093] It is preferable to determine whether to transmit the
RRC-SRS according to states of a cell for which the SRS is
configured or DRX states of the UE. In a state where a SCell is
deactivated, as the SCell does not have to maintain uplink
transmission timing, the need for RRC-SRS transmission is reduced.
During non active time, as there is no need to maintain uplink
transmission timing for the UE, the need for RRC-SRS transmission
is reduced.
[0094] On the other hand, as the L1-SRS is a command issued by the
ENB to repeatedly transmit an SRS for a short time, it may be
unreasonable of the UE to determine whether to transmit the SRS
according to current UE states.
[0095] In the present disclosure, considering SCell and DRX states
described above, the UE does not transmit an RRC-SRS when the SCell
is deactivated or the transmission time belongs to non active time.
Here, when the active time is unexpectedly extended, as described
in connection with the first embodiment, the UE determines whether
to transmit an RRC-SRS by itself in the fourth period. In contrast,
when a PDCCH indicating L1-SRS transmission is received, the UE
transmits an L1-SRS without consideration of active time or SCell
activation states.
[0096] FIG. 7 is a sequence diagram describing UE and ENB
operations according to the second embodiment of the present
disclosure.
[0097] At operation 705, the ENB configures SRS transmission of the
UE for an SCell needing maintenance of uplink transmission timing.
RRC Connection Reconfiguration may contain the following
information. [0098] CyclicShift, srs-Bandwidth, srs-ConfigIndex,
serving cell ID and others [0099] These information elements
indicate a subframe, physical resource block, cycle, and serving
cell to be used for SRS transmission (refer to TS 36.321 for more
detailed information on the above parameters).
[0100] At operation 710, the UE performs RRC-SRS configuration (SRS
based on RRC signaling) and starts SRS transmission from the first
subframe indicated by srs-ConfigIndex demanding SRS transmission.
The UE continues SRS transmission while the serving cell is
activated.
[0101] When a serving cell is activated during DRX active time, the
serving cell is regarded as being activated. That is, an activated
serving cell remains active in the active time of DRX operation
(refer to Section 5.7 and 5.13 of TS 36.321 for more detailed
information on DRX active time and DRX active state).
[0102] At operation 715, the serving cell is deactivated (that is,
the active time expires or MAC CE indicating serving cell
deactivation is received). The UE stops RRC-SRS transmission to the
serving cell.
[0103] At operation 720, the serving cell is activated again. The
UE resumes RRC-SRS transmission to the serving cell.
[0104] At operation 725, the ENB needs uplink channel state
information for the serving cell immediately without time to wait
for next RRC-SRS transmission. To trigger SRS transmission, the ENB
sends an L1 command to the serving cell. The L1 command is sent on
the PDCCH of the serving cell and contains a Carrier Indicator
Field (CIF) indicating a serving cell to send an L1-SRS. The L1
command may contain the following information.
[0105] Number of SRS transmissions, CyclicShift, srs-Bandwidth and
others
[0106] The above information may be signaled to the UE in advance
owing to limited space of the L1 command. In this case, the L1
command may contain only index information indicating a portion of
the pre-signaled information to be used.
[0107] At operation 730, the UE starts L1-SRS transmission to the
indicated serving cell without consideration of activation states
thereof. L1-SRS transmission is started at a subframe closest to
the requested point in time among subframes with configured SRS
resources.
[0108] At operation 735, the UE stops L1-SRS transmission after
reaching the configured number of L1-SRS transmissions.
[0109] At operation 740, the ENB performs uplink scheduling on the
basis of the received L1-SRS transmissions.
[0110] FIG. 8 is a flowchart describing UE operation according to
the second embodiment of the present disclosure.
[0111] At operation 805, the UE receives various configuration
information from the ENB and performs DRX and SRS configuration
accordingly.
[0112] At operation 810, the UE initiates DRX operation and SRS
transmission. When the active time is extended at operation 815,
the UE proceeds to operation 820 at which the UE checks whether the
active time extension is expected or unexpected. Here, unexpected
extension refers to generation of an event extending the active
time within a preset duration preceding the last subframe of the
active time. Expected extension refers to generation of an event
extending the active time before the preset duration preceding the
last subframe of the active time.
[0113] If the extension is expected, the UE proceeds to operation
825 at which the UE continues RRC-SRS transmission and L1-SRS
transmission in the active time. If the extension is unexpected,
the UE proceeds to operation 830 at which the UE checks whether
PUSCH/PUCCH parallel transmission is configured.
[0114] If PUSCH/PUCCH parallel transmission is configured, the UE
proceeds to operation 825. If PUSCH/PUCCH parallel transmission is
not configured, the UE proceeds to operation 835 at which the UE
determines the third period and fourth period. At operation 840,
the UE performs operations in accordance with each period.
[0115] After the fourth period, the UE returns to operation 825 and
continues CSI/SRS transmission during the active time. In the third
period, the UE performs both RRC-SRS transmission and L1-SRS
transmission. In the fourth period, the UE may stop RRC-SRS
transmission and perform L1-SRS transmission, or may perform
RRC-SRS transmission on a best effort basis. That is, if time
enough to prepare RRC-SRS transmission is given between a point in
time when RRC-SRS transmission is known and a point in time when
RRC-SRS transmission is to be performed, the UE performs RRC-SRS
transmission. Otherwise, the UE skips RRC-SRS transmission.
[0116] The ENB receiving CSI/SRS information, as in the case of the
UE, may determine the third period and fourth period and consider
that the UE performs RRC-SRS transmission after the third period
and the fourth period, the UE may or may not perform RRC-SRS
transmission during the fourth period, and, when the third period
is short in particular, occurrence of CSI/SRS transmission is
highly improbable in the former part of the fourth period.
[0117] Here, the sum of the third period length and the fourth
period length is always the same, and the third period length and
the fourth period length may each be varied according to the point
in time when an event extending the active time occurs.
Third Embodiment
[0118] The third embodiment relates to SRS transmission by a UE in
carrier aggregation operation. More specifically, in performing
RRC-SRS and L1-SRS transmission to a SCell, when the active state
of the SCell is extended, the UE may consider whether the active
state extension is expected or unexpected.
[0119] When a SCell is in active state, the SCell is activated and
remains in the DRX active time. During carrier aggregation
operation, a serving cell may be activated or deactivated.
[0120] The PCell is always activated. A SCell is activated in the
case of [0121] Reception of an Activation/Deactivation MAC CE
indicating SCell activation.
[0122] A SCell is activated in the case of [0123] Reception of an
Activation/Deactivation MAC CE indicating SCell deactivation, or
[0124] expiration of the deactivation timer associated with the
SCell.
[0125] The deactivation timer is configured for each Scell. The
deactivation timer is restarted in the case of reception of an
uplink grant for the Scell, reception of a downlink assignment for
the Scell, or reception of an Activation/Deactivation MAC CE
indicating activation of the Scell. Hence, events extending the
active state of a Scell are as follows. [0126] Reception of an
Activation/Deactivation MAC CE indicating activation of an
activated Scell during the DRX active time [0127] Reception of DL
assignment or UL grant for an activated Scell during the DRX active
time
[0128] In the first case, as actual activation operation is
performed after eight subframes from reception of an
Activation/Deactivation MAC CE, there is no issue related to SRS
transmission. However, in the second case, the UE may be unable to
perform SRS transmission if the following situation occurs. [0129]
Reception of an uplink grant or downlink assignment for the Scell
at a subframe closely preceding the subframe n at which the
deactivation timer is scheduled to expire.
[0130] That is, the UE does not prepare SRS transmission under the
assumption that the Scell will be deactivated at the subframe n;
but, due to abrupt extension of the active state of the Scell, the
UE has to perform SRS transmission.
[0131] For effective SRS transmission between the UE and ENB in the
above situation, a strategy similar to that used in the first
embodiment may be utilized. That is, assuming that the active state
is scheduled to end at a subframe n owing to expiration of the
deactivation timer and an event extending the active state occurs
at a subframe n-k, a fifth period, sixth period, seventh period and
eighth period are defined as follows.
[0132] Fifth period: a duration consisting of the subframe n and
x-1 subframes preceding the subframe n. If x is assumed to be 4,
the subframe n-3, subframe n-2, subframe n-1 and subframe n
constitute the fifth period. Reception of a DL assignment or UL
grant for the Scell within the fifth period is described as
unexpected extension of the active state.
[0133] Here, x is a parameter related to processing capabilities to
cope with active state extension. It is preferable for x to have a
single fixed value for all UEs including low end terminals with low
performance.
[0134] Sixth period: when the active state is extended in the fifth
period, a duration consisting of a subframe at which an event
extending the active state (e.g. reception of a DL assignment or UL
grant for the Scell) has occurred and x-1 subframes following the
subframe.
[0135] For example, if an event extending the active state has
occurred at a subframe n-3 and x is 4, the sixth period consists of
the subframe n-3, subframe n-2, subframe n-1 and subframe n. If an
event extending the active state has occurred at a subframe n-2,
the sixth period consists of the subframe n-2, subframe n-1,
subframe n and subframe n+1.
[0136] Seventh period: a duration in which the fifth period and
sixth period overlap each other. That is, the seventh period
consists of the subframes [n-k, n] (from n-k to n, inclusive). The
last subframe of the seventh period is the subframe at which the
active state has been expected to end.
[0137] As the seventh period has already belonged to the active
state before extension of the active state, it is possible to
transmit an SRS regardless of UE processing capabilities. Hence,
determination of whether to transmit an SRS by the UE in the
seventh period may reduce the chance for the ENB to receive an SRS,
causing system performance degradation.
[0138] Eighth period: a duration of the sixth period not
overlapping with the fifth period. That is, the eighth period
consists of the subframes [n+1, n-k+x] (inclusive). The UE may be
able or unable to transmit an RRC-SRS during the eighth period
according to UE capability and the eighth period length.
[0139] For example, as the eighth period length approaches to x
(that is, as the occurrence time of an event extending the active
state becomes closer to the last subframe of the active state), the
possibility of RRC-SRS transmission becomes lower in the former
part of the eighth period and becomes higher in the latter part
thereof. RRC-SRS transmission is possible after the eighth
period.
[0140] For reference, as the UE is aware of a schedule of L1-SRS
transmission before at least four subframes from the scheduled
L1-SRS transmission, the UE is always able to perform L1-SRS
transmission regardless of the above periods.
[0141] When the active state of a Scell is extended, the UE
determines whether the active state extension is expected or
unexpected; if unexpected extension, the UE performs RRC-SRS
transmission in the seventh period, and may not perform RRC-SRS
transmission or perform RRC-SRS transmission on a best effort basis
in the eighth period; and the UE performs RRC-SRS transmission
after the eighth period.
[0142] In other words, assuming that k is an integer between 0 and
x-1, when the active state is extended according to reception of UL
grant or DL assignment for the Scell at the subframe n-k, the UE
normally transmits an RRC-SRS in subframes [n-k, n] corresponding
to the seventh period, may skip RRC-SRS transmission in
subframes[n+1, n+x-k] corresponding to the eighth period, and
normally transmits an RRC-SRS after the subframe n+x-k.
[0143] FIG. 9 is a flowchart describing UE operation according to
the third embodiment of the present disclosure.
[0144] At operation 905, the UE receives various configuration
information from the ENB and performs configurations for DRX, SRS
and carrier aggregation operation accordingly.
[0145] At operation 910, the UE initiates DRX operation, carrier
aggregation operation and SRS transmission. When the active state
of a Scell with RRC-SRS configuration is extended at operation 915,
the UE proceeds to operation 920 at which the UE checks whether the
active state extension is of type 1 or of type 2. The UE proceeds
to operation 925 if type 1 extension, and proceeds to operation 935
if type 2 extension.
[0146] Here, type 1 extension indicates an active state extension
due to reception of Activation/Deactivation MAC CE or reception of
DL assignment or UL grant before the fifth period. Type 2 extension
indicates an active state extension due to reception of DL
assignment or UL grant during the fifth period.
[0147] At operation 925, the UE continues RRC-SRS transmission and
L1-SRS transmission to the Scell. At operation 935, the UE
determines the seventh period and eighth period. At operation 940,
the UE performs operations in accordance with each period. After
the eighth period, the UE returns to operation 925 and continues
SRS transmission in the active state.
[0148] The ENB receiving SRS information for a Scell, as in the
case of the UE, may determine the seventh period and eighth period
and consider that the UE performs RRC-SRS transmission after the
seventh period and the eighth period, the UE may or may not perform
SRS transmission during the eighth period, and, when the seventh
period is short in particular, occurrence of SRS transmission is
highly improbable in the former part of the eighth period.
[0149] Here, the sum of the seventh period length and the eighth
period length is always the same, and the seventh period length and
the eighth period length may each be varied according to the point
in time when an event extending the active state occurs.
[0150] FIG. 10 is a block diagram of a user equipment according to
an embodiment of the present disclosure.
[0151] Referring to FIG. 10, the user equipment may include a
transceiver unit 1005, a control unit 1010, a mux/demux unit 1015,
a control message handler 1030, and various higher layer units 1020
and 1025.
[0152] The transceiver unit 1005 receives data and control signals
through downlink channels of a serving cell and sends data and
control signals through uplink channels. When multiple serving
cells are configured, the transceiver unit 1005 may send and
receive data and control signals through the serving cells.
[0153] The mux/demux unit 1015 multiplexes data coming from the
higher layer units 1020 and 1025 or the control message handler
1030, and demultiplexes data received by the transceiver unit 1005
and forwards the demultiplexed data to the higher layer units 1020
and 1025 or the control message handler 1030.
[0154] The control message handler 1030 processes a control message
received from a base station and performs a corresponding
operation. For example, when DRX related parameters are received,
the control message handler 1030 forwards the same to the control
unit 1010.
[0155] The higher layer units 1020 and 1025 maybe configured on a
service basis. The higher layer units 1020 and 1025 may process
user data generated by service applications such as File Transfer
Protocol (FTP) and Voice over Internet Protocol (VoIP) and forward
the processed user data to the mux/demux unit 1015, and delivers
data coming from the mux/demux unit 1015 to appropriate service
applications at the higher layer.
[0156] The control unit 1010 examines scheduling commands such as
UL grants received through the transceiver unit 1005, and controls
the transceiver unit 1005 and the mux/demux unit 1015 so that
uplink transmissions are performed at proper points in time with
appropriate transmission resources. The control unit 1010 controls
the transceiver unit 1005 for DRX operation and CSI/SRS
transmission.
[0157] FIG. 11 is a block diagram of a base station according to an
embodiment of the present disclosure. The base station of FIG. 11
includes a transceiver unit 1105, a control unit 1110, a mux/demux
unit 1120, a control message handler 1135, various higher layer
units 1125 and 1130, and a scheduler 1115.
[0158] The transceiver unit 1105 sends data and control signals
through a downlink carrier and receives data and control signals
through an uplink carrier. When multiple carriers are configured,
the transceiver unit 1105 may send and receive data and control
signals through the multiple carriers.
[0159] The mux/demux unit 1120 multiplexes data coming from the
higher layer units 1125 and 1130 or the control message handler
1135, and demultiplexes data received by the transceiver unit 1105
and forwards the demultiplexed data to the higher layer units 1125
and 1130, the control message handler 1135 or the control unit
1110. The control message handler 1135 processes a control message
received from a user equipment and performs a corresponding
operation, and generates a control message to be sent to a user
equipment and forwards the control message to a lower layer.
[0160] The higher layer units 1125 and 1130 may be configured on a
terminal and service basis. The higher layer units 1125 and 1130
may process user data generated by service applications such as FTP
and VoIP and forward the processed user data to the mux/demux unit
1120, and process data coming from the mux/demux unit 1120 and
deliver the processed data to service applications at the higher
layer.
[0161] The control unit 1110 determines CSI/SRS transmission times
of user equipments and controls the transceiver unit 1105
accordingly.
[0162] The scheduler 1115 allocates transmission resources to a
user equipment at appropriate points in time in consideration of
buffer states, channel states and active time of the user
equipment, and controls the transceiver unit 1105 to send or
receive a signal to or from the user equipment.
[0163] While the present disclosure has been shown and described
with reference to various embodiments thereof, it should be
understood by those skilled in the art that many variations and
modifications of the method and apparatus described herein will
still fall within the spirit and scope of the present disclosure as
defined in the appended claims and their equivalents.
* * * * *