U.S. patent application number 13/056460 was filed with the patent office on 2011-08-11 for method and apparatus of receiving data in wireless communication system.
Invention is credited to Jae Hoon Chung, Seung Hee Han, So Yeon Kim, Hyun Soo Ko, Moon Il Lee.
Application Number | 20110194514 13/056460 |
Document ID | / |
Family ID | 41610856 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110194514 |
Kind Code |
A1 |
Lee; Moon Il ; et
al. |
August 11, 2011 |
METHOD AND APPARATUS OF RECEIVING DATA IN WIRELESS COMMUNICATION
SYSTEM
Abstract
A method and an apparatus of receiving data in a wireless
communication system. The method includes receiving a downlink (DL)
grant on a physical downlink control channel (PDCCH) through a
first DL component carrier (CC), and receiving data based on the DL
grant through a second DL CC.
Inventors: |
Lee; Moon Il; (Gyeongki-do,
KR) ; Han; Seung Hee; (Gyeongki-do, KR) ; Ko;
Hyun Soo; (Gyeongki-do, KR) ; Chung; Jae Hoon;
(Gyeongki-do, KR) ; Kim; So Yeon; (Gyeongki-do,
KR) |
Family ID: |
41610856 |
Appl. No.: |
13/056460 |
Filed: |
July 30, 2009 |
PCT Filed: |
July 30, 2009 |
PCT NO: |
PCT/KR09/04262 |
371 Date: |
January 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61084992 |
Jul 30, 2008 |
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61226267 |
Jul 16, 2009 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 5/0057 20130101;
H04L 1/1861 20130101; H04L 5/001 20130101; H04L 1/0038 20130101;
H04L 27/2613 20130101; H04L 1/0026 20130101; H04L 5/0055 20130101;
H04L 23/02 20130101; H04L 1/0031 20130101; H04L 5/0053 20130101;
H04L 5/0094 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2008 |
KR |
10-2008-0099671 |
Claims
1-9. (canceled)
10. A method of communication in a wireless communication system,
carried in a user equipment (UE), the method comprising: monitoring
a set of physical downlink control channel (PDCCH) candidates in a
subframe; when a PDCCH candidate is successfully decoded, acquiring
a grant on the successfully decoded PDCCH candidate, the grant
comprising a resource assignment and a component carrier (CC)
indication field, the CC indication field indicating a CC scheduled
for the resource assignment; and receiving or transmitting data
using the resource assignment through the CC indicated by the CC
indication field.
11. The method of claim 10, wherein the PDCCH candidate is
successfully decoded if no CRC error is detected after de-masking
the CRC of the PDCCH candidate with the UE's identifier.
12. The method of claim 11, further comprising: receiving, from a
base station, a message indicating at least one DL CC to monitor
the set of PDCCH candidates.
13. The method of claim 12, wherein the at least one DL CC is
different from the DL CC indicated by the CC indication field.
14. The method of claim 10, further comprising: receiving, from a
base station, a message indicating whether the CC indication field
is present in the grant.
15. The method of claim 14, wherein the message is a radio resource
control (RRC) message.
16. The method of claim 10, wherein a size of the CC indication
field is 3 bits.
17. The method of claim 10, wherein the subframe includes a
plurality of OFDM symbols in time domain and is divided into a
control region and a data region, and the set of PDCCH candidates
is monitored in the control region.
18. A UE comprising: a radio frequency (RF) unit for transmitting
and receiving a radio signal; and a processor operatively coupled
with the RF unit and configured for: monitoring a set of physical
downlink control channel (PDCCH) candidates in a subframe; when a
PDCCH candidate is successfully decoded, acquiring a grant on the
successfully decoded PDCCH candidate, the grant comprising a
resource assignment and a CC indication field, the CC indication
field indicating a CC scheduled for the resource assignment; and
receiving or transmitting data using the resource assignment
through the CC indicated by the CC indication field.
19. The UE of claim 18, wherein the PDCCH candidate is successfully
decoded if no CRC error is detected after de-masking the CRC of the
PDCCH candidate with the UE's identifier.
20. The UE of claim 19, wherein the processor is further configured
for: receiving, from a base station, a message indicating at least
one DL CC to monitor the set of PDCCH candidates.
21. The UE of claim 20, wherein the at least one DL CC is different
from the DL CC indicated by the CC indication field.
22. The UE of claim 18, wherein the processor is further configured
for: receiving, from a base station, a message indicating whether
the CC indication field is present in the grant.
23. The UE of claim 22, wherein the message is a radio resource
control (RRC) message.
24. The UE of claim 18, wherein a size of the CC indication field
is 3 bits.
25. The UE of claim 18, wherein the subframe includes a plurality
of OFDM symbols in time domain and is divided into a control region
and a data region, and the set of PDCCH candidates is monitored in
the control region.
Description
TECHNICAL FIELD
[0001] The present invention relates to wireless communications,
and more particularly, to a method and an apparatus of receiving
data in a wireless communication system.
BACKGROUND ART
[0002] In wireless communication systems, one base station (BS)
generally provides services to a plurality of user equipments
(UEs). The BS schedules user data for the plurality of UEs, and
transmits the user data together with control information
containing scheduling information for the user data. In general, a
channel for carrying the control information is referred to as a
control channel, and a channel for carrying the user data is
referred to as a data channel. The UE finds control information of
the UE by searching for the control channel, and processes data of
the UE by using the control information.
[0003] In order for the UE to receive user data assigned to the UE,
control information for the user data on a control channel must be
received. In a given bandwidth, a plurality of pieces of control
information for a plurality of UEs are generally multiplexed within
one transmission interval. That is, to provide a service to the
plurality of UEs, the BS multiplexes the plurality of pieces of
control information for the plurality of UEs and then transmits the
control information through a plurality of control channels. The UE
searches for control channel of the UE among the plurality of
control channels.
[0004] Blind decoding is one of schemes for detecting specific
control information from the plurality of pieces of multiplexed
control information. The blind decoding attempts to recover a
control channel by using several combinations of information in a
state where a UE has no information required to recover the control
channel. That is, in a state where the UE does not know whether
control information transmitted from the BS is control information
of the UE and the UE does not know in which portion the control
information of the UE exists, the UE decodes all pieces of given
control information until the control information of the UE is
found. The UE can use information unique to each UE to detect the
control information of the UE. For example, when the BS multiplexes
control information of each UE, an identifier unique to each UE can
be transmitted by being masked onto a cyclic redundancy check
(CRC). The CRC is a code used for error detection. The UE de-masks
unique identifier of the UE from the CRC of the received control
information, and then can detect the control information of the UE
by performing CRC checking.
[0005] Meanwhile, as a mobile communication system of a next
generation (i.e., post-3rd generation), an international mobile
telecommunication-advanced (IMT-A) system is standardized aiming at
support of an Internet protocol (IP)-based seamless multimedia
service in an international telecommunication union (ITU) by
providing a high-speed transmission rate of 1 gigabits per second
(Gbps) in downlink communication and 500 megabits per second (Mbps)
in uplink communication. In a 3rd generation partnership project
(3GPP), a 3GPP long term evolution-advanced (LTE-A) system is
considered as a candidate technique for the IMT-A system. The LTE-A
system is evolved to increase a completion level of the LTE system,
and is expected to maintain backward compatibility with the LTE
system. This is because the provisioning of compatibility between
the LTE-A system and the LTE system is advantageous in terms of
user convenience, and is also advantageous for a service provider
since existing equipment can be reused.
[0006] In general, a wireless communication system is a single
carrier system supporting a single carrier. The transmission rate
is proportional to transmission bandwidth. Therefore, for
supporting a high-speed transmission rate, transmission bandwidth
shall be increased. However, except for some areas of the world, it
is difficult to allocate frequencies of wide bandwidths. For
effectively using fragmented small frequency bands, a spectrum
aggregation (also referred to as bandwidth aggregation or carrier
aggregation) technique is being developed. The spectrum aggregation
technique is to obtain the same effect as if which a frequency band
of a logically wide bandwidth may be used by aggregating a
plurality of physically discontiguous frequency bands in a
frequency domain. Through the spectrum aggregation technique,
multiple carrier (multi-carrier) can be supported in the wireless
communication system. The wireless communication system supporting
multi-carrier is referred to as a multi-carrier system. The carrier
may be also referred to as a radio frequency (RF), component
carrier (CC), etc.
[0007] Accordingly, there is a need for a method and an apparatus
of effectively receiving data in a multi-carrier system.
DISCLOSURE OF INVENTION
Technical Problem
[0008] The present invention provides a method and an apparatus of
receiving data in a wireless communication system.
Solution to Problem
[0009] In an aspect, a method of receiving data in a wireless
communication system, carried in a user equipment (UE), is
provided. The method includes receiving a downlink (DL) grant on a
physical downlink control channel (PDCCH) through a first DL
component carrier (CC) from a base station (BS), and receiving data
based on the DL grant through a second DL CC from the BS.
[0010] Preferably, the DL grant comprises a CC indication field
indicating the second DL CC.
[0011] Preferably, a cyclic redundancy check (CRC) of the DL grant
is scrambled with a UE identifier (ID), and the UE ID indicates the
second DL CC.
[0012] Preferably, an index of a control channel element (CCE)
indicates the second DL CC, the CCE is used for transmitting the
PDCCH.
[0013] The method may further includes receiving a second DL grant
on a second PDCCH through the first DL CC from the BS, and
receiving second data based on the second DL grant through a third
DL CC.
[0014] In another aspect, a method of transmitting data in a
wireless communication system, carried in a UE, is provided. The
method includes receiving a uplink (UL) grant on a PDCCH through a
first DL CC from a BS, and transmitting data based on the UL grant
through a first UL CC to the BS.
[0015] Preferably, the UL grant comprises a CC indication field
indicating the first UL CC.
[0016] In still another aspect, a UE is provided. The UE includes a
radio frequency (RF) unit transmitting and/or receiving a radio
signal and a processor coupled with the RF unit and configured to
receive a DL grant on a PDCCH through a first DL CC, and receive
data based on the DL grant through a second DL CC.
[0017] Preferably, the DL grant comprises a CC indication field
indicating the second DL CC.
Advantageous Effects of Invention
[0018] A method and an apparatus of effectively receiving data are
provided. Accordingly, overall system performance can be
improved.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a block diagram showing a wireless communication
system.
[0020] FIG. 2 shows an example of a plurality of component carriers
(CCs) used in a multi-carrier system.
[0021] FIG. 3 is a block diagram showing an example of a
multi-carrier system.
[0022] FIG. 4 shows an example of a plurality of physical channels
(PHYs).
[0023] FIG. 5 shows an example of a bandwidth used by a PHY.
[0024] FIG. 6 shows an example of an asymmetric structure of
downlink and uplink in a multi-carrier system.
[0025] FIG. 7 shows a structure of a radio frame.
[0026] FIG. 8 shows an example of a resource grid for one downlink
slot.
[0027] FIG. 9 shows a structure of a radio frame and a subframe in
a frequency division duplex (FDD) system.
[0028] FIG. 10 shows an example of an resource element group (REG)
structure when a base station (BS) uses one or two transmit (Tx)
antennas.
[0029] FIG. 11 shows an example of an REG structure when a BS uses
four Tx antennas.
[0030] FIG. 12 shows an example of mapping of a physical control
format indicator channel (PCFICH) to REGs.
[0031] FIG. 13 is a flow diagram showing an example of a method of
transmitting data and receiving data performed by a user equipment
(UE).
[0032] FIG. 14 is a flowchart showing an example of a method of
configuring a physical downlink control channel (PDCCH).
[0033] FIG. 15 shows an example of a method of multiplexing a
plurality of PDCCHs for a plurality of UEs, performed by a BS.
[0034] FIG. 16 shows an example of a method of monitoring a control
channel, performed by a UE.
[0035] FIG. 17 shows an example of a PDCCH transmission method in a
multi-carrier system.
[0036] FIG. 18 is a flow diagram showing method of receiving data,
performed by a UE, according to an embodiment of the present
invention.
[0037] FIG. 19 is a flow diagram showing method of transmitting
data, performed by a UE, according to another embodiment of the
present invention.
[0038] FIG. 20 illustrates a method of configuring a
multi-PDCCH.
[0039] FIG. 21 shows an example in which a multi-PDCCH is
transmitted in a multi-carrier system.
[0040] FIG. 22 shows another example in which a multi-PDCCH is
transmitted in a multi-carrier system.
[0041] FIG. 23 shows still another example in which a multi-PDCCH
is transmitted in a multi-carrier system.
[0042] FIG. 24 shows an example in which PDCCHs are transmitted in
a multi-carrier system.
MODE FOR THE INVENTION
[0043] FIG. 1 is a block diagram showing a wireless communication
system.
[0044] Referring to FIG. 1, a wireless communication system 10
includes at least one base station (BS) 11. The BSs 11 provide
communication services to specific geographical regions (generally
referred to as cells) 15a, 15b, and 15c. The cell can be divided
into a plurality of regions (referred to as sectors). A user
equipment (UE) 12 may be fixed or mobile, and may be referred to as
another terminology, such as a mobile station (MS), a user terminal
(UT), a subscriber station (SS), a wireless device, a personal
digital assistant (PDA), a wireless modem, a handheld device, etc.
The BS 11 is generally a fixed station that communicates with the
UE 12 and may be referred to as another terminology, such as an
evolved node-B (eNB), a base transceiver system (BTS), an access
point, etc.
[0045] Hereinafter, a downlink (DL) denotes communication from the
BS to the UE, and an uplink (UL) denotes communication from the UE
to the BS. In the DL, a transmitter may be a part of the BS, and a
receiver may be a part of the UE. In the UL, the transmitter may be
a part of the UE, and the receiver may be a part of the BS.
[0046] The wireless communication system supports multi-antenna.
The transmitter may use a plurality of transmit (Tx) antennas, and
the receiver may use a plurality of receive (Rx) antennas. The Tx
antenna is a logical or physical antenna used to transmit one
signal or one stream, and the Rx antenna is a logical or physical
antenna used to receive one signal or one stream.
[0047] If the transmitter and the receiver use multi-antenna, the
wireless communication system may be called as multiple input
multiple output (MIMO) system.
[0048] FIG. 2 shows an example of a plurality of component carriers
(CCs) used in a multi-carrier system.
[0049] Referring to FIG. 2, a multi-carrier system may use N CCs
(CC #1, CC #2, . . . , CC #N). Although it is described herein that
adjacent CCs are physically discontiguous in a frequency domain,
this is for exemplary purposes only. Adjacent CCs may be physically
contiguous in a frequency domain
[0050] Therefore, a frequency band of a logically wide bandwidth
may be used in the multi-carrier system by aggregating a plurality
of physically discontiguous and/or contiguous CCs in a frequency
domain.
[0051] In downlink, a BS concurrently can transmit information to
one UE through one or more CCs. In uplink, the UE can also transmit
data to the BS through one or more CCs.
[0052] FIG. 3 is a block diagram showing an example of a
multi-carrier system.
[0053] Referring to FIG. 3, each of a transmitter 100 and a
receiver 200 uses N CCs (CC #1, CC #2, . . . , CC #N) in a
multi-carrier system. A CC includes one or more physical channels
(hereinafter, simply referred to as PHYs). A wireless channel is
established between the transmitter 100 and the receiver 200.
[0054] The transmitter 100 includes a plurality of PHYs 110-1, . .
. , 110-M, a multi-carrier multiplexer 120, and a plurality of Tx
antennas 190-1, . . . , 190-Nt. The receiver 200 includes a
multi-carrier demultiplexer 210, a plurality of PHYs 220-1, . . . ,
220-L, and a plurality of Rx antennas 290-1, . . . , 290-Nr. The
number M of PHYs of the transmitter 100 may be identical to or
different from the number L of PHYs of the receiver 200. Although
it is described herein that each of the transmitter 100 and the
receiver 200 includes a plurality of antennas, this is for
exemplary purposes only. The transmitter 100 and/or the receiver
200 includes a single antenna.
[0055] The transmitter 100 generates Tx signals from information
based on the N CCs, and the Tx signals are transmitted on M PHYs
110-1, . . . , 110-M. The multi-carrier multiplexer 120 combines
the Tx signals so that the Tx signals can be simultaneously
transmitted on the M PHYs. The combined Tx signals are transmitted
through the Nt Tx antennas 190-1, . . . , 190-Nt. The Tx radio
signals are received through the Nr Rx antennas 290-1, . . . ,
290-Nr of the receiver 200 through the wireless channel. The Rx
signals are de-multiplexed by the multi-carrier demultiplexer 210
so that the Rx signals are separated into the L PHYs 220-1, . . . ,
220-L. Each of the PHYs 220-1, . . . , 220-L recovers the
information.
[0056] The multi-carrier system may include one or more carrier
modules. The carrier module upconverts a baseband signal to a
carrier frequency to be modulated onto a radio signal, or
downconverts a radio signal to recover a baseband signal. The
carrier frequency is also referred to as a center frequency. The
multi-carrier system may use a plurality of carrier modules for
each carrier frequency, or use a carrier module which can change a
carrier frequency.
[0057] FIG. 4 shows an example of a plurality of PHYs. FIG. 4 shows
an example of N CCs consisting of M PHYs (PHY #1, PHY #2, . . . ,
PHY #M).
[0058] Referring to FIG. 4, each of M PHYs has a specific bandwidth
(BW). An PHY #m has a center frequency f.sub.c,m and a bandwidth of
N.sub.IFFT,m.times..DELTA.f.sub.m (where m=1, . . . , M). Herein,
N.sub.IFFT,m denotes an inverse fast Fourier transform (IFFT) size
of the PHY #m, and .DELTA.f.sub.m denotes a subcarrier spacing of
the PHY #m. The IFFT size and the subcarrier spacing may be
different or identical for each PHY. Center frequencies of the
respective PHYs may be arranged with a regular interval or an
irregular interval.
[0059] According to a UE or a cell, each PHY may use a bandwidth
narrower than a maximum bandwidth. For example, if it is assumed
that each PHY has a maximum bandwidth of 20 mega Hertz (MHz), and M
is 5, then a full bandwidth of up to 100 MHz can be supported.
[0060] FIG. 5 shows an example of a bandwidth used by a PHY.
[0061] Referring to FIG. 5, if it is assumed that a maximum
bandwidth of the PHY is 20 MHz, the PHY can use a bandwidth (e.g.,
10 MHz, 5 MHz, 2.5 MHz, or 1.25 MHz) narrower than the maximum
bandwidth. Regardless of a bandwidth size used by the PHY in
downlink, a synchronization channel (SCH) may exist in each PHY.
The SCH is a channel for cell search. The cell search is a
procedure by which a UE acquires time synchronization and frequency
synchronization with a cell and detects a cell identifier (ID) of
the cell. If the SCH is located in all downlink PHYs, all UEs can
be synchronized with the cell. In addition, if a plurality of
downlink PHYs are allocated to the UE, cell search may be performed
for each PHY or may be performed only for a specific PHY.
[0062] As such, a UE or a BS can transmit and/or receive
information based on one or more PHYs in the multi-carrier system.
The number of PHYs used by the UE may be different from or equal to
the number of PHYs used by the BS. In general, the BS can use M
PHYs, and the UE can use L PHYs (M.gtoreq.L, where M and L are
natural numbers). Herein, L may differ depending on a type of the
UE.
[0063] The multi carrier system can have several types of uplink
and downlink configurations. In a frequency division duplex (FDD)
system or a time division duplex (TDD) system, a structure of
downlink and uplink may be an asymmetric structure in which an
uplink bandwidth and a downlink bandwidth are different from each
other. Alternatively, the structure of downlink and uplink may be
configured in which an uplink bandwidth and a downlink bandwidth
are identical to each other. In this case, the structure of
downlink and uplink may be configured to a symmetric structure in
which the same number of PHYs exist in both uplink and downlink
transmissions or an asymmetric structure in which the number of PHY
differs between uplink and downlink transmissions.
[0064] FIG. 6 shows an example of an asymmetric structure of
downlink and uplink in a multi-carrier system. A transmission time
interval (TTI) is a scheduling unit for information transmission.
In each of the FDD system and the TDD system, a structure of
downlink and uplink is an asymmetric structure. If the structure of
downlink and uplink is an asymmetric structure, a specific link may
have a higher information throughput. Therefore, system can be
optimized flexibly.
[0065] Hereinafter, for convenience of explanation, it is assumed
that a CC includes one PHY.
[0066] All transmission/reception methods used in a single carrier
system using can also be applied to each CC of the transmitter and
the receiver in a multi-carrier system. In addition, it is
desirable for the multi-carrier system to maintain backward
compatibility with the single carrier system which is legacy system
of the multi-carrier system, This is because the provisioning of
compatibility between the multi-carrier system and the single
carrier system is advantageous in terms of user convenience, and is
also advantageous for a service provider since existing equipment
can be reused.
[0067] Now, a single carrier system will be described.
[0068] FIG. 7 shows a structure of a radio frame.
[0069] Referring to FIG. 7, the radio frame consists of 10
subframes. One subframe consists of two slots. Slots included in
the radio frame are numbered with slot numbers #0 to #19. A time
required to transmit one subframe is defined as a TTI. For example,
one radio frame may have a length of 10 milliseconds (ms), one
subframe may have a length of 1 ms, and one slot may have a length
of 0.5 ms.
[0070] The structure of the radio frame is for exemplary purposes
only, and thus the number of subframes included in the radio frame
or the number of slots included in the subframe may change
variously.
[0071] FIG. 8 shows an example of a resource grid for one downlink
slot.
[0072] Referring to FIG. 8, the downlink slot includes a plurality
of orthogonal frequency division multiplexing (OFDM) symbols in a
time domain and NDL resource blocks (RBs) in a frequency domain.
The OFDM symbol is for expressing one symbol period, and may be
referred to as an orthogonal frequency division multiple access
(OFDMA) symbol or a single carrier-frequency division multiple
access (SC-FDMA) symbol according to a multiple access scheme. The
number N.sup.DL of resource blocks included in the downlink slot
depends on a downlink transmission bandwidth configured in a cell.
One RB includes a plurality of subcarriers in the frequency
domain.
[0073] Each element on the resource grid is referred to as a
resource element (RE). Although it is described herein that one RB
includes 7.times.12 resource elements consisting of 7 OFDM symbols
in the time domain and 12 subcarriers in the frequency domain for
example, the number of OFDM symbols and the number of subcarriers
in the RB are not limited thereto. Thus, the number of OFDM symbols
and the number of subcarriers may change variously depending on a
cyclic prefix (CP) length, a subcarrier spacing, etc. For example,
when using a normal CP, the number of OFDM symbols is 7, and when
using an extended CP, the number of OFDM symbols is 6.
[0074] The resource grid for one downlink slot of FIG. 8 can be
applied to a resource grid for an uplink slot.
[0075] FIG. 9 shows a structure of a radio frame and a subframe in
a FDD system.
[0076] Referring to FIG. 9, the radio frame includes 10 subframes,
and each subframe includes two consecutive slots. When using a
normal CP, the subframe includes 14 OFDM symbols. When using an
extended CP, the subframe includes 12 OFDM symbols. A SCH is
transmitted in every radio frame. The SCH includes a primary
(P)-SCH and a secondary (S)-SCH. The P-SCH is transmitted through a
last OFDM symbol of a 1st slot of a subframe 0 and a subframe 5 in
a radio frame. When using the normal CP, the P-SCH is an OFDM
symbol 6 in the subframe, and when using the extended CP, the P-SCH
is an OFDM symbol 5 in the subframe. The S-SCH is transmitted
through an OFDM symbol located immediately before an OFDM symbol on
which the P-SCH is transmitted.
[0077] A maximum of three OFDM symbols (i.e., OFDM symbols 0, 1,
and 2) located in a front portion of a 1st slot in every subframe
correspond to a control region. The remaining OFDM symbols
correspond to a data region. A physical downlink shared channel
(PDSCH) can be assigned to the data region. Downlink data is
transmitted on PDSCH.
[0078] Cntrol channels such as a physical control format indicator
channel (PCFICH), a physical HARQ (hybrid automatic repeat request)
indicator channel (PHICH), a physical downlink control channel
(PDCCH) etc., can be assigned to the control region.
[0079] Resource element groups (REGs) are used for defining the
mapping of a control channel to resource elements.
[0080] FIG. 10 shows an example of an REG structure when a BS uses
one or two Tx antennas. FIG. 11 shows an example of an REG
structure when a BS uses four Tx antennas. In FIGS. 10 and 11, it
is assumed that a maximum of three OFDM symbols (i.e., OFDM symbols
0, 1, and 2) located in a front portion of a 1st slot in a subframe
are control regions.
[0081] Referring to FIGS. 10 and 11, Rp indicates a resource
element which is used to transmit a reference signal (hereinafter
referred to as an `RS`) through antenna p (p.epsilon.{0, 1, 2, 3}).
The RS may be also referred to as a pilot. One REG is composed of
four adjacent resource elements in the frequency domain other than
resource elements which are used for RS transmission. In the OFDM
symbol 0 in the subframe, two REGs exist within one resource block
in the frequency domain. It is to be noted that the above REG
structures are only illustrative and the number of resource
elements included in the REG may change in various ways.
[0082] The PHICH carries an HARQ acknowledgement
(ACK)/not-acknowledgement (NACK) for uplink data.
[0083] The PCFICH carries information about the number of OFDM
symbols used for transmission of PDCCHs in a subframe. Although the
control region includes three OFDM symbols herein, this is for
exemplary purposes only. According to an amount of control
information, the PDCCH is transmitted through the OFDM symbol 0, or
the OFDM symbols 0 and 1, or the OFDM symbols 0 to 2. The number of
OFDM symbols used for PDCCH transmission may change in every
subframe. The PCFICH is transmitted through a 1st OFDM symbol
(i.e., the OFDM symbol 0) in every subframe. The PCFICH can be
transmitted through a single antenna or can be transmitted through
a multi-antenna using a transmit diversity scheme. When a subframe
is received, the UE evaluates control information transmitted
through the PCFICH, and then receives control information
transmitted through the PDCCH.
[0084] The control information transmitted through the PCFICH is
referred to as a control format indicator (CFI). For example, the
CFI may have a value of 1, 2, or 3. The CFI value may represent the
number of OFDM symbols used for PDCCH transmission in a subframe.
That is, if the CIF value is 2, the number of OFDM symbols used for
PDCCH transmission in a subframe is 2. This is for exemplary
purposes only, and thus information indicated by the CFI may be
defined differently according to a downlink transmission bandwidth.
For example, if the downlink transmission bandwidth is less than a
specific threshold value, the CFI values of 1, 2, and 3 may
indicate that the number of OFDM symbols used for PDCCH
transmission in the subframe is 2, 3, and 4, respectively.
[0085] The following table shows an example of a CFI and a 32-bit
CFI codeword which generates by performing channel coding to the
CFI.
[0086] Table 1
TABLE-US-00001 TABLE 1 CFI codeword CFI <b.sub.0, b.sub.1, . . .
, b.sub.31> 1 <0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1> 2 <1, 0,
1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,
1, 0, 1, 1, 0, 1, 1, 0> 3 <1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1> 4
<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, (Reserved) 0, 0, 0, 0, 0, 0, 0, 0, 0>
[0087] The 32-bit CFI codeword can be mapped to a 16 modulated
symbols using a quadrature phase shift keying (QPSK) scheme. In
this case, 16 resource elements (or subcarriers) are used in PCFICH
transmission. That is, 4 REGs are used in PCFICH transmission.
[0088] FIG. 12 shows an example of mapping of a PCFICH to REGs.
[0089] Referring to FIG. 12, the PCFICH is mapped to 4 REGs, and
the respective REGs to which the PCFICH are mapped are spaced apart
from one another. An REG to which the PCFICH is mapped may vary
according to the number of resource blocks in a frequency domain.
In order to avoid inter-cell interference of the PCFICH, the REGs
to which the PCFICH is mapped may be shifted in a frequency domain
according to a cell ID.
[0090] Now, a PDCCH will be described.
[0091] A control region consists of a set of control channel
elements (CCEs). The CCEs are indexed 0 to N(CCE)-1, where N(CCE)
is the total number of CCEs constituting the set of CCEs in a
downlink subframe. The CCE corresponds to a plurality of REGs. For
example, one CCE may correspond to 9 REGs. A PDCCH is transmitted
on an aggregation of one or several consecutive CCEs. A PDCCH
format and the possible number of bits of the PDCCH are determined
according to the number of CCEs constituting the CCE aggregation.
Hereinafter, the number of CCEs constituting the CCE aggregation
used for PDCCH transmission is referred to as a CCE aggregation
level. In addition, the CCE aggregation level is a CCE unit for
searching for the PDCCH. A size of the CCE aggregation level is
defined by the number of contiguous CCEs. For example, the CCE
aggregation level may be an element of {1, 2, 4, 8}.
[0092] The following table shows an example of the PDCCH format,
the number of REGs and the number of PDCCH bits.
[0093] Table 2
TABLE-US-00002 TABLE 2 Number of PDCCH format CCE aggregation level
Number of REGs PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72
576
[0094] Control information transmitted on the PDCCH is referred to
as downlink control information (DCI). The DCI transports uplink
scheduling information, downlink scheduling information, or an
uplink power control command, etc. The downlink scheduling
information is also referred to as a downlink grant, and the uplink
scheduling information is also referred to as an uplink grant.
[0095] FIG. 13 is a flow diagram showing an example of a method of
transmitting data and receiving data performed by a UE.
[0096] Referring to FIG. 13, a BS transmits an uplink grant to a UE
at step S11. The UE transmits uplink data to the BS based on the
uplink grant at step S12. The uplink grant may be transmitted on a
PDCCH, and the uplink data may be transmitted on a physical uplink
shared channel (PUSCH). A relationship between a subframe in which
a PDCCH is transmitted and a subframe in which a PUSCH is
transmitted may be previously set between the BS and the UE. For
example, if the PDCCH is transmitted in an nth subframe in a FDD
system, the PUSCH may be transmitted in an (n+4)th subframe.
[0097] The BS transmits an downlink grant to the UE at step S13.
The UE receives downlink data from the BS based on the downlink
grant at step S14. The downlink grant may be transmitted on a
PDCCH, and the downlink data may be transmitted on a PDSCH. For
example, the PDCCH and the PDSCH are transmitted in the same
subframe.
[0098] As described above, a UE shall receive DCI on PDCCH to
receive downlink data from a BS or transmit uplink data to a
BS.
[0099] DCI may use a different DCI format in accordance with usage.
For example, a DCI format for an uplink grant and a DCI format for
a downlink grant is different each other. A size and usage of DCI
may differ according to a DCI format.
[0100] The following table shows an example of the DCI format.
[0101] Table 3
TABLE-US-00003 TABLE 3 DCI format Objectives 0 Scheduling of PUSCH
1 Scheduling of one PDSCH codeword 1A Compact scheduling of one
PDSCH codeword 1B Closed-loop single-rank transmission 1C Paging,
RACH response and dynamic BCCH 1D MU-MIMO 2 Scheduling of
closed-loop rank-adapted spatial multiplexing mode 2A Scheduling of
open-loop rank-adapted spatial multiplexing mode 3 TPC commands for
PUCCH and PUSCH with 2 bit power adjustments 3A TPC commands for
PUCCH and PUSCH with single bit power adjustments
[0102] Referring to above table, a DCI format 0 is used for PUSCH
scheduling. The DCI format 0 is used for an uplink grant.
[0103] A DCI format 1 is used for scheduling of one PDSCH codeword.
A DCI format 1A is used for compact scheduling of one PDSCH
codeword. A DCI format 1B is used for compact scheduling of one
PDSCH codeword in a closed-loop rank 1 transmission mode. A DCI
format 1C is used for paging, random access channel (RACH)
response, and dynamic broadcast control channel (BCCH). A DCI
format 1D is used for PDSCH scheduling in a multi-user (MU)-MIMO
mode. A DCI format 2 is used for PDSCH scheduling in a closed-loop
rank-adapted spatial multiplexing mode. A DCI format 2A is used for
PDSCH scheduling in an open-loop rank-adapted spatial multiplexing
mode. Each of from DCI format 1 to DCI format 2A is used for a
downlink grant. However, the DCI format may differ according to a
usage of DCI or transmission mode of a BS.
[0104] DCI formats 3 and 3A are used for transmission of a
transmission power control (TPC) command for a physical uplink
control channel (PUCCH) and a PUSCH. The DCI formats 3 and 3A is
used for an uplink power control command.
[0105] Each DCI format consists of a plurality of information
fields. The type of information fields constituting a DCI format,
the size of each of the information fields, etc. may differ
according to the DCI format. For example, a downlink grant (or an
uplink grant) includes resource allocation field indicating radio
resource. The downlink grant (or the uplink grant) may include
further a modulation and coding scheme (MCS) field indicating
modulation scheme and channel coding sheme. In addition, the
downlink grant (or the uplink grant) may include further various
information fields.
[0106] FIG. 14 is a flowchart showing an example of a method of
configuring a PDCCH.
[0107] Referring to FIG. 14, in step S21, a BS generates
information bit stream in accordance with a DCI format. In step
S22, the BS attaches a cyclic redundancy check (CRC) for error
detection to the information bit stream. The information bit stream
may be used to calculate the CRC. The CRC is parity bits, and the
CRC may be attached in front of the information bit stream or at
the back of the information bit stream.
[0108] The CRC is masked with an identifier (referred to as a radio
network temporary identifier (RNTI)) according to an owner or usage
of the DCI. The masking may be scrambling of the CRC with the
identifier. The masking may be an modulo 2 operation or exclusive
or (XOR) operation between the CRC and the identifier.
[0109] If the DCI is for a specific UE, a unique identifier (e.g.,
cell-RNTI (C-RNTI)) of the UE may be masked onto the CRC. The
C-RNTI may be also referred to as a UE ID. The CRC can be masked
with different RNTI except C-RNTI, such as paging-RNTI (P-RNTI) for
a paging message, system information-RNTI (SI-RNTI) for system
information, random access-RNTI (RA-RNTI) for indicating random
access response which is response of random access preamble
transmitted by a UE, etc.
[0110] In step S23, the BS generates coded bit stream by performing
channel coding to the information bit stream attached the CRC. The
channel coding scheme is not limited. For example, convolution
coding scheme can be used. The number of PDCCH bits may differ in
accordance with channel coding rate.
[0111] In step of S24, the BS generates rate matched bit stream by
performing rate matching to the coded bit stream. In step of S25,
the BS generates modulated symbols by modulating the rate matched
bit stream. In step of S26, the BS maps the modulated symbols to
resource elements.
[0112] As described above, a method of configuring one PDCCH is
explained. However, a plurality of control channels may be
transmitted in a subframe. That is, a plurality of PDCCHs for
several UEs can be transmitted by being multiplexed in one
subframe. Generation of information bit stream, CRC attachment,
channel coding, and rate matching, etc. are performed independently
for each PDCCH. The aforementioned process of configuring the PDCCH
of FIG. 14 can be performed independently for each PDCCH.
[0113] FIG. 15 shows an example of a method of multiplexing a
plurality of PDCCHs for a plurality of UEs, performed by a BS.
[0114] Referring to FIG. 15, a CCE set constituting a control
region in a subframe is constructed of a plurality of CCEs indexed
from 0 to N(CCE)-1. That is, the number of CCEs is N(CCE). A PDCCH
for a UE #1 is transmitted on a CCE aggregation with a CCE index 0
at a CCE aggregation level of 1. A PDCCH for a UE #2 is transmitted
on a CCE aggregation with a CCE index 1 at a CCE aggregation level
of 1. A PDCCH for a UE #3 is transmitted on a CCE aggregation with
CCE indices 2 and 3 at a CCE aggregation level of 2. A PDCCH for a
UE #4 is transmitted on a CCE aggregation with CCE indices 4, 5, 6,
and 7 at a CCE aggregation level of 4. A PDCCH for a UE #5 is
transmitted on a CCE aggregation with CCE indices 8 and 9 at a CCE
aggregation level of 2.
[0115] The CCEs are mapped to resource elements (REs) according to
a CCE-to-RE mapping rule. In this case, a PDCCH of each UE is
mapped to the REs by being interleaved in the control region in the
subframe. Locations of the REs to be mapped may change according to
the number of OFDM symbols used for transmission of the PDCCHs in
the subframe, the number of PHICH groups, the number of Tx
antennas, and the frequency shifts.
[0116] The BS does not provide the UE with information indicating
where a PDCCH of the UE is located in the subframe. In general, in
a state where the UE does not know a location of the PDCCH of the
UE in the subframe, the UE finds the PDCCH of the UE by monitoring
a set of PDCCH candidates in every subframe. Monitoring implies
that the UE attempts decoding each of the PDCCH candidates
according to all the monitored DCI formats. This is referred to as
blind decoding or blind detection. If no CRC error is detected if
the UE performs CRC checking after de-masking C-RNTI from a PDCCH
candidate, it is regarded that the PDCCH candidate is detected by
the UE as the PDCCH of the UE.
[0117] In addition, the UE does not know at which CCE aggregation
level the PDCCH of the UE is transmitted. Therefore, the UE needs
to attempt decoding on the set of PDCCH candidates for each of all
possible CCE aggregation levels.
[0118] FIG. 16 shows an example of a method of monitoring a control
channel, performed by a UE.
[0119] Referring to FIG. 16, a CCE set constituting a control
region in a subframe is constructed of a plurality of CCEs indexed
from 0 to N(CCE)-1. That is, the number of CCEs is N(CCE). There
are four types of a CCE aggregation level L, that is, {1, 2, 4, 8}.
A set of PDCCH candidates monitored by the UE is differently
defined according to the CCE aggregation level. For example, if the
CCE aggregation level is 1, the PDCCH candidates correspond to all
CCEs constituting the CCE set. If the CCE aggregation level is 2,
the PDCCH candidates correspond to a CCE aggregation with CCE
indices 0 and 1, a CCE aggregation with CCE indices 2 and 3, and so
on. If the CCE aggregation level is 4, the PDCCH candidates
correspond to a CCE aggregation with CCE indices 0 to 3, a CCE
aggregation with CCE indices 4 to 7, and so on. If the CCE
aggregation level is 8, the PDCCH candidates correspond to a CCE
aggregation with CCE indices 0 to 7, and so on.
[0120] A frame structure of a single carrier system, a PDCCH
transmission and monitoring method, etc., have been described
above. For optimization of a multi-carrier system, a multi-antenna
scheme or a control channel shall be designed by considering a
frequency channel property for each CC. Therefore, it is important
to properly use a system parameter and an optimal
transmission/reception scheme for each CC. In addition, the same
frame structure as a legacy system may be used in one CC of the
multi-carrier system. In this case, the control channel shall be
properly modified to operate both a UE for the legacy system and a
UE for the multi-carrier system. Hereinafter, the UE for the legacy
system is referred to as a long term evolution (LTE) UE, and the UE
for the multi-carrier system is referred to as an LTE-advanced
(LTE-A) UE.
[0121] FIG. 17 shows an example of a PDCCH transmission method in a
multi-carrier system.
[0122] Referring to FIG. 17, a UE uses two downlink component
carriers (DL CCs) CC #1 and CC #2. In a type 1, the BS can transmit
a PDCCH to the UE through several DL CCs. The PDCCH transmitted
through the CC #1 may carry the scheduling information of downlink
data which is transmitted through the CC #1 or may carry the
scheduling information of downlink data which is transmitted
through the CC #2. That is, the scheduling information of downlink
data which is transmitted through one of a plurality of DL CCs may
be transmitted over the plurality of DL CCs. Accordingly, in the
type 1, the PDCCH can obtain a frequency diversity gain. However,
if the channel state of a specific DL CC is not good, the PDCCH
transmitted through the specific DL CC may not be detected. In this
case, the UE may not receive downlink data which is transmitted
through a PDSCH corresponding to the PDCCH.
[0123] In a type 2, the BS can transmit a PDCCH to the UE through
only any one of several DL CCs. In the type 2, limited radio
resources can be efficiently used because a control region through
which the PDCCH is transmitted is integrated. However, if the
channel state of a specific DL CC through which the PDCCH is
transmitted is not good, the UE may not receive downlink data
through other DL CCs.
[0124] In a type 3, the BS uses an independent PDCCH in each of
several DL CCs. A
[0125] PDCCH transmitted through one DL CC may carry the scheduling
information of downlink data which is transmitted through the one
DL CC, but does not carry the scheduling information of downlink
data which is transmitted through other DL CCs. The type 3 is very
flexible. Further, although the channel state of a specific DL CC
is poor, the UE can receive downlink data through other DL CCs.
Accordingly, the type 3 has a robust system characteristic.
However, if the same control information is repeated every DL CC,
unnecessary overhead may occur.
[0126] In the type 1 or type 2, when one or more PDCCHs are
transmitted for one LTE-A UE, the PDCCHs can be transmitted through
DL CCs different from DL CCs through which PDSCHs corresponding to
the PDCCHs are transmitted. Accordingly, it becomes a problem that
a PDCCH carries control information which is associated with which
one of several DL CCs.
[0127] FIG. 18 is a flow diagram showing method of receiving data,
performed by a UE, according to an embodiment of the present
invention.
[0128] Referring to FIG. 18, a UE receives a downlink grant on a
PDCCH through a first DL CC from a BS (step S110). The UE receives
data based on the downlink grant through a second DL CC from the BS
(step S120).
[0129] The UE further receives a second downlink grant on a second
PDCCH through the first DL CC from the BS. The UE further receives
second data based on the second downlink grant through a third DL
CC.
[0130] FIG. 19 is a flow diagram showing method of transmitting
data, performed by a UE, according to another embodiment of the
present invention.
[0131] Referring to FIG. 19, a UE receives an uplink grant on a
PDCCH through a first DL CC from a BS (step S210). The UE transmits
data based on the uplink grant through a first UL CC to the BS
(step S220).
[0132] Hereinafter, carrier information which indicates a CC
associated with a PDCCH is described. The BS can inform the UE of
the carrier information through a variety of methods.
[0133] (1) Method of Adding a CC Indication Bit Field (CIBF) when
Generating an Information Bit Stream
[0134] A CIBF can be added to each DCI format as an information
field.
[0135] The following table lists examples of CCs indicated by
respective CIBF according to respective CIBF values.
[0136] Table 4
TABLE-US-00004 TABLE 4 CIBF CARRIER NUMBER 00 CC #1 01 CC #2 10 CC
#3 11 CC #4
[0137] Referring to above table, a UE can use four CCs (CC #1, CC
#2, CC #3, and CC #4), and the size of a CIBF may be 2 bits. It is,
however, to be noted that the above table is only illustrative, and
the size of the CIBF and the CCs indicated by the respective CIBFs
may be configured in various ways.
[0138] Further, the size of a CIBF may be previously defined
between a UE and a BS. Alternatively, a BS may inform a UE of the
size of a CIBF through higher layer signaling such as a radio
resource control (RRC) signaling. Further, the size of a CIBF may
be determined according to a UE. For example, the size of a CIBF
may be determined according to the number of CCs used by a UE.
[0139] The size of a CIBF may be determined according to a DCI
format. In the case of a DCI format for an uplink grant (e.g., a
DCI format 0), the size of a CIBF may be determined according to
the number of UL CCs which are used by a UE. The CIBF of a DCI
format for an uplink grant may be referred to as an uplink (UL)
CIBF. The size of a CIBF which is included in a DCI format for a
downlink grant may be determined according to the number of DL CCs
which are used by a UE. The CIBF of a DCI format for a downlink
grant may be referred to as a downlink (DL) CIBF. Accordingly, the
size of a UL CIBF may differ from the size of a DL CIBF.
Furthermore, the size of a CIBF may vary according to a service
type, a transmission mode, etc. of a DCI format. The service type
can be classified into semi-persistent scheduling (SPS) for
transmitting voice over internet protocol (VoIP), etc., dynamic
scheduling, and so on. The transmission mode may be classified into
one antenna transmission scheme, a transmission diversity scheme,
an open-loop spatial multiplexing scheme, a closed-loop spatial
multiplexing scheme, a multi-user (MU)-MIMO scheme, and so on. For
example, in the case of a DCI format for the open-loop spatial
multiplexing scheme, all CCs are not used, but only some of the CCs
are used. Accordingly, a DCI format may not include the CIBF, or
the size of the CIBF may be small.
[0140] In the case where a UE uses a plurality of CCs, the CIBF can
be applied to all PDCCHs. In the case where a UE uses only one CC,
the CIBF may be reserved or may be used for other purposes.
Alternatively, when an information bit stream is generated, the
CIBF may not be included.
[0141] (2) Method of Masking Carrier Information to CRC
[0142] A BS can indicate carrier information through a specific
masking pattern for the CRC of a PDCCH. A UE can determine that the
PDCCH is for which CC based on the CRC masking pattern of the
PDCCH. For example, a UE identifier (ID) can be used in order to
mask carrier information to CRC.
[0143] A LTE UE is assigned with one UE ID in a cell. A method of
assigning a UE ID to a LTE-A UE may be various. A method of
assigning a UE ID to a LTE-A UE is described below.
[0144] First, a BS may assign a CC-specific UE ID to each UE. That
is, a BS assigns an independent UE ID to a UE on a CC basis. A UE
is assigned a plurality of UE IDs, and the number of UE IDs is
identical to the number of CC. A BS masks a CC-based UE ID to the
CRC of control information which will be transmitted to a UE. For
example, a UE can detect a PDCCH based on a UE ID for a CC #2 in a
CC #1. The UE can receive downlink data which is transmitted
through the CC #2 on the basis of the PDCCH. Although a UE ID is
assigned to each LTE-A UE on a CC basis, a BS can efficiently
assign a limited number of UE IDs to a number of LTE-A UEs by
assigning a different number of CCs to each of the LTE-A UEs.
However, this method may increase signaling overhead for UE ID
assignment because the UE ID is assigned to each UE on a CC
basis.
[0145] Second, a BS may assign a UE ID to each UE on the basis of a
CC set. In the case where a BS assigns m CCs to a LTE-A UE, the BS
may classify the m number of CCs into n CC sets and may assign a UE
ID to each of the n CC sets (where m.gtoreq.n). The LTE-A UE is
assigned the n number of UE IDs. Here, one CC may belong to only
one CC set. A BS may flexibly assign a UE ID according to the
number of available UE IDs within a cell. Further, when the m
number of CCs is classified into the n number of CC sets, "n" can
be changed according to time in order to assign the UE IDs more
efficiently. The n number of CC sets may be constructed of the m
number of CCs in several forms, such as physical layer (or layer 1)
signaling or medium access control (MAC) layer (or layer 2)
signaling.
[0146] Third, a BS may assign a cell-specific UE ID to a LTE-A UE.
A UE performs blind decoding on a PDCCH using always the same UE ID
irrespective of CCs assigned thereto. In this case, signaling for
UE ID assignment can be simplified. However, the UE cannot
determine that the PDCCH is for which CC based on a UE ID which has
been masked to a CRC of the PDCCH. Accordingly, the BS must inform
the UE of carrier information through another method.
[0147] (3) Method of Implicitly Indicating Carrier Information
[0148] A BS may implicitly inform a LTE-A UE of carrier
information. For example, a LTE-A UE can determine which PDCCH is
for which CC based on the first control channel element (CCE) index
of a CCE aggregation on which the PDCCH is transmitted and/or the
CCE aggregation level. However, there is a high probability that
carrier information may have error if the UE does not receive a
specific PDCCH.
[0149] In accordance with the methods (1) to (3) of a BS informing
a UE of carrier information, the carrier information may
dynamically change every subframe.
[0150] (4) Method of Transmitting Carrier Information Through RRC
Signaling
[0151] A BS may semi-statically transmit carrier information to a
UE through RRC signaling. In this case, the carrier information may
be semi-statically changed.
[0152] As described above, since the BS informs the UE of the
carrier information, the UE can receive downlink data or transmit
uplink data on the basis of a PDCCH after receiving the PDCCH. The
BS can transmit downlink data to the UE on the PDSCH on the basis
of a plurality of CCs. The UE must be able to receive a PDCCH
corresponding to the number of CCs in order to read the downlink
data which is transmitted on the PDSCH on the basis of the
plurality of CCs.
[0153] However, a BS may transmit, to a UE, a PDCCH used for the
scheduling of a PDSCH through a DL CC which is different from a DL
CC through which the PDSCH is transmitted. Accordingly, a number of
PDCCHs for one UE can be transmitted through one DL CC. A number of
the PDCCHs may be for different CCs. A number of the PDCCHs are
hereinafter referred to as a multi-PDCCH. The multi-PDCCH is a kind
of PDCCH set including a plurality of PDCCHs for one UE and is
transmitted through one CC. A BS may configure one multi-PDCCH or a
plurality of multi-PDCCHs for one UE. Accordingly, in the case
where a UE uses a plurality of DL CCs, one or more of the plurality
of DL CCs each may use for multi-PUCCH transmission.
[0154] FIG. 20 illustrates a method of configuring a
multi-PDCCH.
[0155] Referring to FIG. 20, the multi-PDCCH includes two PDCCHs
(PDCCH #1 and PDCCH #2). It is, however, to be noted that the above
example is only illustrative and the multi-PDCCH may include three
or more PDCCHs.
[0156] A BS generates a first information bit stream according to a
DCI format of the PDCCH #1 and generates a second information bit
stream according to a DCI format of the PDCCH #2 at step S310. The
DCI format of the PDCCH #1 and the DCI format of the PDCCH #2 may
be the same or may differ from each other. In other words, the DCI
format of the PDCCH #1 and the DCI format of the PDCCH #2 may be
independent from each other. The first information bit stream and
the second information bit stream may include respective CIBFs.
[0157] The BS attaches a CRC #1 to the first information bit stream
and a CRC #2 to the second information bit stream at step S320. A
UE ID #1 is masked to the CRC #1, and a UE ID #2 is masked to the
CRC #2. The UE ID #1 and the UE ID #2 may be the same or may differ
from each other. In the case where the UE ID #1 and the UE ID #2
differ from each other, the UE ID #1 may indicate a CC for the
PDCCH #1 and the UE ID #2 may indicate a CC for the PDCCH #2.
[0158] A CRC may be applied to each of PDCCHs constituting a
multi-PDCCH. Alternatively, a CRC may be applied to only a
multi-PDCCH. For example, a CRC of a multi-PDCCH may be attached to
a bit stream in which a first information bit stream and a second
information bit stream are combined. For another example, a CRC may
be applied to both a multi-PDCCH and each PDCCH. For example, a CRC
of a multi-PDCCH may be further attached to a bit stream in which a
first information bit stream to which a CRC #1 has been attached
and a second information bit stream to which a CRC #2 has been
attached are combined. Here, the length of the CRC applied to each
PDCCH and the length of the CRC applied to the multi-PDCCH may
differ from each other.
[0159] A joint coding method or a separate coding method can be
used as a channel coding method for multi-PDCCH configuration. In
the joint coding method, bit streams in each of which information
bit streams corresponding to respective PDCCHs are combined are
subject to channel coding together. A UE can obtain plural pieces
of control information through single channel decoding. In the
separate coding method, information bit streams corresponding to
respective PDCCHs are individually subject to channel coding,
thereby generating respective coded bit streams. A multi-PDCCH can
be configured by packing a plurality of coded bit streams. Here,
PDCCHs constituting the multi-PDCCH preferably have the same
channel coding rate.
[0160] CCE aggregations on which respective PDCCHs constituting a
multi-PDCCH are transmitted may be consecutive to each other or may
be separated from each other.
[0161] FIG. 21 shows an example in which a multi-PDCCH is
transmitted in a multi-carrier system.
[0162] Referring to FIG. 21, the multi-PDCCH for a UE #1 is
transmitted through a CC #1. PDCCHs constituting the multi-PDCCH
are for different CCs.
[0163] FIG. 22 shows another example in which a multi-PDCCH is
transmitted in a multi-carrier system.
[0164] Referring to FIG. 22, each of PDCCHs constituting the
multi-PDCCH includes a CIBF indicative of carrier information. The
multi-PDCCH for a UE #1 is transmitted through a CC #1. Here, the
multi-PDCCH includes a PDCCH for the CC #1 and a PDCCH for a CC #2.
A PDCCH for the UE #1 is transmitted through a CC #L.
[0165] A CC through which a multi-PDCCH is transmitted is described
below.
[0166] A multi-PDCCH may be transmitted through only a specific CC
(refer to FIG. 21). This method corresponds to the method of
transmitting a multi-PDCCH according to the type 2 of FIG. 17.
Alternatively, a multi-PDCCH may be transmitted through any one of
a plurality of CCs. This method corresponds to the method of
transmitting a multi-PDCCH according to the type 1 of FIG. 17.
Here, in order to maximize a frequency diversity gain, a CC through
which a multi-PDCCH is transmitted may be changed into a specific
pattern according to the hopping rule which is previously agreed
between a BS and a UE.
[0167] In an alternative method, the transmission method according
to the type 1 and the transmission method according to the type 2
may be adaptively used according to channel condition. For example,
a UE which is in a high-speed mobile environment is difficult to
determine which CC has a good channel condition. In this case, the
UE may transmit a multi-PDCCH according to the type 1. Here, a CC
through which the multi-PDCCH is transmitted can be determined in
accordance with the hopping rule. Accordingly, a frequency
diversity gain can be obtained. On the other hand, a UE which is in
a low-speed mobile environment can determine which CC has a good
channel condition through a variety of feedback channels. The UE
may select a specific CC according to time and transmit a
multi-PDCCH through the selected CC. Here, a BS must inform the UE
of information about the CC through which the multi-PDCCH is
transmitted.
[0168] A CC set through which a multi-PDCCH is transmitted may be
configured. For example, in the case where a UE uses an L number of
CCs, the multi-PDCCH can be transmitted through only a CC set which
is defined to be the N number of CCs (N<L). Accordingly, the
complexity of blind decoding of a UE can be reduced. Here, a number
of PDCCHs may be distributed and transmitted through respective CCs
within the CC set. Information about a CC set may be previously
defined, or a UE may be informed of information about a CC set
through RRC signaling.
[0169] FIG. 23 shows still another example in which a multi-PDCCH
is transmitted in a multi-carrier system.
[0170] Referring to FIG. 23, a multi-PDCCH for a UE #1 is
transmitted through a CC #1. PDCCHs are not transmitted through a
CC #2. That is, only a PDSCH can be transmitted through the CC
#2.
[0171] As described above, in the case where a multi-PDCCH is
transmitted, CCs through which PDCCHs are not transmitted, but
through which only PDSCHs can be transmitted can be configured. A
CC through which only a PDSCH can be transmitted can be used along
with other CC through which a PDCCH associated with the PDSCH is
transmitted. Further, in the case where a CC through which only a
PDSCH can be transmitted is configured, a UE may be configured not
to transmit or receive any information during a specific subframe
transmitted through the CC.
[0172] FIG. 24 shows an example in which PDCCHs are transmitted in
a multi-carrier system.
[0173] Referring to FIG. 24, a UE uses an L number of DL CCs (DL CC
#1, DL CC #2, . . . , DL CC #L) and a U number of UL CCs (UL CC #1,
UL CC #2, . . . , UL CC #U). When the L number of DL CCs is the
same as the U number of UL CCs, the DL CCs and the UL CCs have a
symmetric structure. When the L number of DL CCs is different from
the U number of UL CCs, the DL CCs and the UL CCs have an
asymmetric structure.
[0174] A BS transmits three PDCCHs to a UE through the DL CC #1.
One of the three PDCCHs is for the DL CC #1, another of the three
PDCCHs is for the DL CC #L, and yet another of the three PDCCHs is
for the UL CC #2. Each of the PDCCHs may include a CIBF indicating
carrier information. In the case where the L number of DL CCs
differs from the U number of UL CCs, the size of a UL CIBF may
differ from the size of a DL CIBF. For example, in the case where
the U number of UL CCs is smaller than the L number of DL CCs, the
size of a UL CIBF may be smaller than the size of a DL CIBF.
[0175] FIG. 25 shows an example in which CC subsets are set.
[0176] Referring to FIG. 25, a UE may be assigned with an L number
of DL CCs (DL CC #1, DL CC #2, . . . , DL CC #L). A CC super set
includes the L number of DL CCs. A CC subset including the DL CC #2
and the DL CC #L may be set from the CC super set. It is, however,
to be noted that the above example is only illustrative and a CC
subset may be set from a CC super set in various ways. A UE may use
only DL CCs included in a CC subset.
[0177] The number of DL CCs required for the UE to which the L
number of DL CCs has been assigned may vary according to channel
condition or a service type. However, if the L number of DL CCs is
always set for a UE, the UE must monitor all the DL CCs and measure
channels for all the DL CCs. It makes the UE unnecessarily consume
its power. Accordingly, if a CC subset is set, a UE has only to
monitor only DL CCs belonging to the CC subset and to measure
channels for the DL CCs. In this case, unnecessary calculation
complexity and power consumption in the UE can be reduced.
[0178] A BS may inform the UE of information about the CC subset
through RRC signaling, a PDCCH, a broadcast message, or the like.
Information about the CC subset may indicate CCs which constitute
the CC subset using a bitmap. If a bitmap is used, flexibility in
setting a CC subset can be increased.
[0179] It is hereinafter assumed that a UE uses a CC subset and a
PDCCH includes a CIBF.
[0180] In order to reduce the size of the CIBF, the CIBF may
indicate CCs on the basis of the CC subset not a CC super set. An
example in which, as in FIG. 25, the CC subset includes DL CC #2
and DL CC #L is described below. For example, when the CIBF of a
PDCCH is 2, the PDCCH is for the DL CC #L. In the case where the UE
does not use the CC subset, the PDCCH having the CIBF of 2 is for
the DL CC #2. However, in order to reduce complexity, a CIBF may
always have the same size irrespective of whether a CC subset is
used or not.
[0181] Although DL CCs have so far been described, UL CCs may also
be limited to a CC subset.
[0182] The length of a CP in each CC is described below.
[0183] In a multi-carrier system, CCs have the same subframe
length, but have different center frequencies. In particular, in
the case where adjacent CCs are physically discontinuous in the
frequency domain, channel characteristics between the CCs may
differ. Furthermore, each of the CCs may have different delay
spread. Accordingly, CPs having different lengths may be used every
CC or every CC set. The number of OFDM symbols within one subframe
changes according to the length of a CP. A case in which a first CC
with an SCH and a second CC without an SCH are assigned to one UE
is hereinafter assumed. The UE can find the length of a CP of the
first CC through the SCH. The UE can obtain the length of a CP of
the second CC through RRC signaling which is transmitted through
the first CC or a control channel, such as a PDCCH transmitted
through the first CC.
[0184] FIG. 26 is a block diagram showing wireless communication
system to implement an embodiment of the present invention. A BS 50
may include a processor 51, a memory 52 and a radio frequency (RF)
unit 53. The processor 51 may be configured to implement proposed
functions, procedures and/or methods described in this description.
Layers of the radio interface protocol may be implemented in the
processor 51. The memory 52 is operatively coupled with the
processor 51 and stores a variety of information to operate the
processor 51. The RF unit 53 is operatively coupled with the
processor 11, and transmits and/or receives a radio signal. A UE 60
may include a processor 61, a memory 62 and a RF unit 63. The
processor 61 may be configured to implement proposed functions,
procedures and/or methods described in this description. The memory
62 is operatively coupled with the processor 61 and stores a
variety of information to operate the processor 61. The RF unit 63
is operatively coupled with the processor 61, and transmits and/or
receives a radio signal.
[0185] The processors 51, 61 may include application-specific
integrated circuit (ASIC), other chipset, logic circuit, data
processing device and/or converter which converts a baseband signal
into a radio signal and vice versa. The memories 52, 62 may include
read-only memory (ROM), random access memory (RAM), flash memory,
memory card, storage medium and/or other storage device. The RF
units 53, 63 include one or more antennas which transmit and/or
receive a radio signal. When the embodiments are implemented in
software, the techniques described herein can be implemented with
modules (e.g., procedures, functions, and so on) that perform the
functions described herein. The modules can be stored in memories
52, 62 and executed by processors 51, 61. The memories 52, 62 can
be implemented within the processors 51, 61 or external to the
processors 51, 61 in which case those can be communicatively
coupled to the processors 51, 61 via various means as is known in
the art.
[0186] As described above, in a multi-carrier system, a BS can
efficiently transmit a PDCCH. A UE can receive downlink data or
transmit uplink data efficiently on the basis of a PDCCH. A method
and an apparatus of effectively receiving data are provided.
Further, backward compatibility with a single carrier system can be
maintained. Accordingly, an overall system performance can be
improved.
[0187] In view of the exemplary systems described herein,
methodologies that may be implemented in accordance with the
disclosed subject matter have been described with reference to
several flow diagrams. While for purposed of simplicity, the
methodologies are shown and described as a series of steps or
blocks, it is to be understood and appreciated that the claimed
subject matter is not limited by the order of the steps or blocks,
as some steps may occur in different orders or concurrently with
other steps from what is depicted and described herein. Moreover,
one skilled in the art would understand that the steps illustrated
in the flow diagram are not exclusive and other steps may be
included or one or more of the steps in the example flow diagram
may be deleted without affecting the scope and spirit of the
present disclosure.
[0188] What has been described above includes examples of the
various aspects. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the various aspects, but one of ordinary skill in the
art may recognize that many further combinations and permutations
are possible. Accordingly, the subject specification is intended to
embrace all such alternations, modifications and variations that
fall within the spirit and scope of the appended claims.
* * * * *