U.S. patent application number 13/056451 was filed with the patent office on 2011-06-16 for method and apparatus of monitoring pdcch 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 | 20110143796 13/056451 |
Document ID | / |
Family ID | 41610856 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110143796 |
Kind Code |
A1 |
Lee; Moon Il ; et
al. |
June 16, 2011 |
METHOD AND APPARATUS OF MONITORING PDCCH IN WIRELESS COMMUNICATION
SYSTEM
Abstract
A method and an apparatus of monitoring a physical downlink
control channel (PDCCH) in a wireless communication system, carried
in a user equipment (UE), are provided. The method includes
receiving a PDCCH map, and monitoring a set of PDCCH candidates
based on the PDCCH map.
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.: |
13/056451 |
Filed: |
July 30, 2009 |
PCT Filed: |
July 30, 2009 |
PCT NO: |
PCT/KR09/04264 |
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: |
455/507 |
Current CPC
Class: |
H04L 1/0031 20130101;
H04L 5/0055 20130101; H04L 1/0026 20130101; H04L 1/1861 20130101;
H04L 5/0057 20130101; H04L 27/2613 20130101; H04L 1/0038 20130101;
H04L 5/001 20130101; H04L 23/02 20130101; H04L 5/0053 20130101;
H04L 5/0094 20130101 |
Class at
Publication: |
455/507 |
International
Class: |
H04B 7/24 20060101
H04B007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2008 |
KR |
10-2008-0099671 |
Claims
1-10. (canceled)
11. A method of monitoring a physical downlink control channel
(PDCCH) in a wireless communication system, carried in a user
equipment (UE), the method comprising: receiving, from a base
station (BS), a PDCCH map comprising a monitoring set field
indicating a monitoring set comprising N downlink (DL) component
carriers (CCs) among L DL CCs, where L.gtoreq.N, L and N each is a
natural number; and monitoring a set of PDCCH candidates at each of
the N DL CCs.
12. The method of claim 11, wherein the step of monitoring a set of
PDCCH candidates includes: decoding each PDCCH candidate; and if a
PDCCH candidate is successfully decoded, acquiring control
information on the successfully decoded PDCCH candidate.
13. The method of claim 12, wherein the PDCCH candidate is
successfully decoded if no CRC error is detected after de-masking
the CRC of the PDCCH candidate with a UE's identifier.
14. The method of claim 13, wherein the PDCCH map further comprises
a CCE field, the CCE field indicating the Y CCE aggregation levels
among X CCE aggregation levels, where X.gtoreq.Y, X and Y each is a
natural number.
15. The method of claim 14, wherein the UE monitors the set of
PDCCH candidates at each of Y control channel element (CCE)
aggregation levels.
16. The method of claim 11, wherein the PDCCH map is received on a
PDCCH.
17. The method of claim 11, wherein the PDCCH map is received
through a specific DL CC among the L DL CCs.
18. The method of claim 11, wherein the PDCCH map is received
through a DL CC, the DL CC being changed among the L DL CCs in
accordance with a predefined rule.
19. The method of claim 11, wherein the PDCCH map is received via a
radio resource control (RRC) message.
20. A UE comprising: radio frequency (RF) unit transmitting and
receiving a radio signal; and a processor coupled with the RF unit
and configured to receive, from a base station (BS), a PDCCH map
comprising a monitoring set field indicating a monitoring set
comprising N downlink (DL) component carriers (CCs) among L DL CCs,
where L.gtoreq.N, L and N each is a natural number, and to monitor
a set of PDCCH candidates at each of the N DL CCs.
21. The UE of claim 20, wherein the processor is further configured
to; decode each PDCCH candidate; and if a PDCCH candidate is
successfully decoded, acquire control information on the
successfully decoded PDCCH candidate.
22. The UE of claim 21, 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.
23. The UE of claim 22, wherein the PDCCH map further comprises a
CCE field, the CCE field indicating the Y CCE aggregation levels
among X CCE aggregation levels, where X.gtoreq.Y, X and Y each is a
natural number.
24. The UE of claim 23, wherein the processor monitors the set of
PDCCH candidates at each of the Y control channel element (CCE)
aggregation levels.
25. The UE of claim 20, wherein the PDCCH map is received on a
PDCCH.
26. The UE of claim 20, wherein the PDCCH map is received through a
specific DL CC among the L DL CCs.
27. The UE of claim 20, wherein the PDCCH map is received through a
DL CC, the DL CC being changed among the L DL CCs in accordance
with a predefined rule.
28. The UE of claim 20, wherein the PDCCH map is received via a
radio resource control (RRC) message.
Description
TECHNICAL FIELD
[0001] The present invention relates to wireless communications,
and more particularly, to a method and an apparatus of monitoring a
physical downlink control channel (PDCCH) 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] However, if a BS transmits a control channel and a UE
monitors the control channel with a same manner used in a single
carrier system in a multi-carrier system, the complexity of blind
decoding is significantly increased.
[0008] Accordingly, there is a need for a method and an apparatus
of effectively transmitting a control channel and monitoring a
control channel in a multi-carrier system.
DISCLOSURE OF INVENTION
Technical Problem
[0009] The present invention provides a method and an apparatus of
monitoring a physical downlink control channel (PDCCH) in a
wireless communication system.
Technical Solution
[0010] In an aspect, a method of monitoring a physical downlink
control channel (PDCCH) in a wireless communication system, carried
in a user equipment (UE), is provided. The method includes
receiving a PDCCH map from a base station (BS), and monitoring a
set of PDCCH candidates based on the PDCCH map.
[0011] Preferably, the PDCCH map comprises a monitoring set field,
the monitoring set field indicating N downlink component carriers
(CCs) out of L downlink CCs (L.gtoreq.N, where L and N each is a
natural number), and a UE monitors the set of PDCCH candidates in
each of the N downlink CC.
[0012] Preferably, the PDCCH map is received on a PDCCH.
[0013] Preferably, the PDCCH map is received through a constant
downlink CC out of a plurality of downlink CCs.
[0014] Preferably, the PDCCH map is received through a downlink CC,
the downlink CC is hopped among a plurality of downlink CCs in
accordance with a hopping rule.
[0015] Preferably, the PDCCH map is received via radio resource
control (RRC) signal.
[0016] Preferably, the PDCCH map comprises a control channel
element (CCE) field, the CCE field indicating Y CCE aggregation
levels out of X CCE aggregation levels (X.gtoreq.Y, where X and Y
each is a natural number), and a UE monitors the set of PDCCH
candidates at each of the Y CCE aggregation levels.
[0017] Preferably, the PDCCH map comprises a monitoring set field
and a CCE field.
[0018] In 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 PDCCH map, and monitor a set of PDCCH candidates based on the
PDCCH map.
[0019] In still another aspect, a method of transmitting a PDCCH in
a wireless communication system, carried in a BS, is provided. The
method includes transmitting a PDCCH map to a UE, and transmitting
a PDCCH in accordance with the PDCCH map to the UE.
Advantageous Effects
[0020] A method and an apparatus of effectively monitoring a
physical downlink control channel (PDCCH) are provided.
Accordingly, overall system performance can be improved.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a block diagram showing a wireless communication
system.
[0022] FIG. 2 shows an example of a plurality of component carriers
(CCs) used in a multi-carrier system.
[0023] FIG. 3 is a block diagram showing an example of a
multi-carrier system.
[0024] FIG. 4 shows an example of a plurality of physical channels
(PHYs).
[0025] FIG. 5 shows an example of a bandwidth used by a PHY.
[0026] FIG. 6 shows an example of an asymmetric structure of
downlink and uplink in a multi-carrier system.
[0027] FIG. 7 shows a structure of a radio frame.
[0028] FIG. 8 shows an example of a resource grid for one downlink
slot.
[0029] FIG. 9 shows a structure of a radio frame and a subframe in
a frequency division duplex (FDD) system.
[0030] FIG. 10 shows an example of an resource element group (REG)
structure when a base station (BS) uses one or two transmit (Tx)
antennas.
[0031] FIG. 11 shows an example of an REG structure when a BS uses
four Tx antennas.
[0032] FIG. 12 shows an example of mapping of a physical control
format indicator channel (PCFICH) to REGs.
[0033] FIG. 13 is a flow diagram showing an example of a method of
transmitting data and receiving data performed by a user equipment
(UE).
[0034] FIG. 14 is a flowchart showing an example of a method of
configuring a physical downlink control channel (PDCCH).
[0035] FIG. 15 shows an example of a method of multiplexing a
plurality of PDCCHs for a plurality of UEs, performed by a BS.
[0036] FIG. 16 shows an example of a method of monitoring a control
channel, performed by a UE.
[0037] FIG. 17 shows an example of a PDCCH transmission method in a
multi-carrier system.
[0038] FIG. 18 is a flow diagram showing a control channel
transmission method and/or a control channel monitoring method
according to an embodiment of the present invention.
[0039] FIG. 19 shows an example of transmitting a PDCCH by using a
PDCCH map in a multi-carrier system.
[0040] FIG. 20 shows another example of transmitting a PDCCH by
using a PDCCH map in a multi-carrier system.
[0041] FIG. 21 shows an example of semi-statically configured a
PDCCH map.
[0042] FIG. 22 shows another example of semi-statically configured
a PDCCH map.
[0043] FIG. 23 shows a control channel monitoring method performed
by a UE in a multi-carrier system.
[0044] FIG. 24 is a block diagram showing wireless communication
system to implement an embodiment of the present invention.
MODE FOR THE INVENTION
[0045] FIG. 1 is a block diagram showing a wireless communication
system.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] If the transmitter and the receiver use multi-antenna, the
wireless communication system may be called as multiple input
multiple output (MIMO) system.
[0050] FIG. 2 shows an example of a plurality of component carriers
(CCs) used in a multi-carrier system.
[0051] 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
[0052] 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.
[0053] 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.
[0054] FIG. 3 is a block diagram showing an example of a
multi-carrier system.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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).
[0060] 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 M.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.
[0061] 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.
[0062] FIG. 5 shows an example of a bandwidth used by a PHY.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] Hereinafter, for convenience of explanation, it is assumed
that a CC includes one PHY.
[0068] 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.
[0069] Now, a single carrier system will be described.
[0070] FIG. 7 shows a structure of a radio frame.
[0071] 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.
[0072] 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.
[0073] FIG. 8 shows an example of a resource grid for one downlink
slot.
[0074] 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 NDL 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.
[0075] 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.
[0076] The resource grid for one downlink slot of FIG. 8 can be
applied to a resource grid for an uplink slot.
[0077] FIG. 9 shows a structure of a radio frame and a subframe in
a FDD system.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] Resource element groups (REGs) are used for defining the
mapping of a control channel to resource elements.
[0082] 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.
[0083] 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.
[0084] The PHICH carries an HARQ acknowledgement
(ACK)/not-acknowledgement (NACK) for uplink data.
[0085] 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.
[0086] 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.
[0087] The following table shows an example of a CFI and a 32-bit
CFI codeword which generates by performing channel coding to the
CFI.
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, (Reserved) 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
[0088] 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.
[0089] FIG. 12 shows an example of mapping of a PCFICH to REGs.
[0090] 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.
[0091] Now, a PDCCH will be described.
[0092] 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}.
[0093] The following table shows an example of the PDCCH format,
the number of REGs and the number of PDCCH bits.
TABLE-US-00002 TABLE 2 PDCCH CCE Number Number format aggregation
level of REGs of 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.
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
[0101] Referring to above table, a DCI format 0 is used for PUSCH
scheduling. The DCI format 0 is used for an uplink grant.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] FIG. 14 is a flowchart showing an example of a method of
configuring a PDCCH.
[0106] 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.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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.
[0112] FIG. 15 shows an example of a method of multiplexing a
plurality of PDCCHs for a plurality of UEs, performed by a BS.
[0113] 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.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] FIG. 16 shows an example of a method of monitoring a control
channel, performed by a UE.
[0118] 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.
[0119] 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.
[0120] FIG. 17 shows an example of a PDCCH transmission method in a
multi-carrier system.
[0121] Referring to FIG. 17, the multi-carrier system uses a
plurality of CCs, i.e., CC #1, CC #2, . . . , CC #L. A PDCCH for a
UE #1 is transmitted for each CC in every subframe. The UE #1 has
to attempt blind decoding to find the PDCCH of the UE #1 for each
CC in every subframe.
[0122] Therefore, if L downlink CCs are used in the multi-carrier
system, the LTE-A UE has to receive the PDCCH with a reception
complexity which is L times higher than that of the LTE UE. This
causes a problem of great power consumption in the LTE-A. To solve
this problem, there is a need for an effective control channel
transmission method and control channel monitoring method in the
multi-carrier system, whereby a reception complexity of the control
channel can be minimized according to a scheduling condition or a
channel condition.
[0123] FIG. 18 is a flow diagram showing a control channel
transmission method and/or a control channel monitoring method
according to an embodiment of the present invention.
[0124] Referring to FIG. 18, a BS transmits a PDCCH map to a UE
(step S110). The UE monitors a set of PDCCH candidates based on the
PDCCH map (step S120).
[0125] To decrease a blind decoding complexity of the UE, the PDCCH
map includes information regarding a PDCCH transmitted by the BS to
the UE. The PDCCH map may include a monitoring set field and/or a
CCE field. The PDCCH map may be configured differently in
accordance with each DCI format
[0126] First, the monitoring set field is described.
[0127] If a UE uses L downlink CCs, a BS can transmit a PDCCH
simultaneously through N downlink CCs out of the L downlink CCs
(L.gtoreq.N, where L and N are natural numbers). In this case, when
the BS informs the UE of the N downlink CCs on which the PDCCH is
transmitted, the UE performs blind decoding only in the N downlink
CCs. Accordingly, a blind decoding complexity of the UE can be
decreased. That is, the monitoring set field indicates the N
downlink CCs out of the L downlink CCs. The BS transmits the PDCCH
to the UE only through the N downlink CCs. The UE monitors the
PDCCH only in the N downlink CCs. That is, the UE monitors a set of
PDCCH candidates in each of the N downlink CCs. The monitoring set
field may be configured differently in accordance with each DCI
format.
[0128] FIG. 19 shows an example of transmitting a PDCCH by using a
PDCCH map in a multi-carrier system.
[0129] Referring to FIG. 19, the PDCCH map includes a monitoring
set field. The PDCCH map is transmitted only through a CC #1. The
PDCCH map is dynamically transmitted in every subframe. If the
PDCCH map is dynamically transmitted, flexibility of scheduling can
be increased. The PDCCH map transmission method of FIG. 19 is for
exemplary purposes only, and the PDCCH map transmission method of
the present invention is not limited thereto.
[0130] Hereinafter, a radio resource for transmitting a PDCCH map
will be described. The radio resource used for PDCCH map
transmission may be constructed by combining a time resource, a
frequency resource, and/or a code resource. The radio resource by
which the PDCCH map is transmitted may be determined according to a
rule predetermined between a BS and a UE. Alternatively, the PDCCH
map may be transmitted in a PDCCH format. That is, in a state where
the UE does not know a location of the PDCCH map in a subframe, the
UE can attempt blind decoding to find a PDCCH map in every
subframe. For example, the PDCCH map may be generated in such a
manner that an information bit stream based on the PDCCH map format
is generated and then an identifier (ID) of the UE, which is an
owner of the PDCCH map, is masked to a CRC. The PDCCH map format
may include a monitoring set field and/or a CCE field as an
information field.
[0131] Even if the PDCCH map is transmitted in the PDCCH format, it
is preferable that the UE knows a downlink CC on which the PDCCH
map is transmitted. This is because a purpose of transmitting the
PDCCH map is to reduce the blind decoding complexity, and this
purpose is not achieved if the UE does not know the downlink CC on
which the PDCCH map is transmitted.
[0132] Hereinafter, a CC on which a PDCCH map is transmitted will
be described.
[0133] A BS can transmit the PDCCH map to a UE through a constant
downlink CC. Alternatively, the downlink CC on which the PDCCH map
is transmitted may change over time. For example, the downlink CC
on which the PDCCH map is transmitted may change with a specific
period according to a channel condition. Alternatively, the
downlink CC on which the PDCCH map is transmitted may change in a
specific pattern according to a hopping rule predetermined between
the BS and the UE. In this case, the PDCCH map can be transmitted
by being distributed over a plurality of downlink CCs. In another
method, the BS may configure a downlink CC on which the PDCCH map
is transmitted semi-statically through higher layer signaling such
as a radio resource control (RRC) signaling. In this case, the
downlink CC on which the PDCCH map is transmitted is
semi-statically modified.
[0134] The downlink CC on which the PDCCH map is transmitted may be
determined according to the UE. A plurality of downlink CCs to be
allocated may differ according to the UE. The UE can use a downlink
CC of a lowest frequency band among the plurality of allocated
downlink CCs in transmission of the PDCCH map. This is because a
low frequency band has a high reliability.
[0135] If the PDCCH is not transmitted in all downlink CCs, the BS
may transmit the PDCCH map to the UE to report a presence or
absence of the PDCCH. Alternatively, the BS may not transmit the
PDCCH map to the UE, which can be regarded as error occurrence.
[0136] FIG. 20 shows another example of transmitting a PDCCH by
using a PDCCH map in a multi-carrier system.
[0137] Referring to FIG. 20, the multi-carrier system uses three
downlink CCs, i.e., CC #1, CC #2, and CC #3. The PDCCH map includes
a monitoring set field. A PDCCH map of a UE #1 is transmitted
through the CC #1 in every subframe. In a subframe n, a monitoring
set field for the UE #1 indicates the CC #1, the CC #2, and the CC
#3. Therefore, the PDCCHs for the UE #1 are transmitted through
each of the CC #1, the CC #2, and the CC #3. In a subframe n+1, the
monitoring set field for the UE #1 indicates the CC #2. Therefore,
the PDCCH for the UE #1 is transmitted only through the CC #2. In a
subframe n+k, the monitoring set field for the UE #1 indicates the
CC #1 and the CC #3. Therefore, the PDCCHs for the UE #1 are
transmitted through each of the CC #1 and the CC #3.
[0138] The monitoring set field may use a bitmap to indicate a
downlink CC on which a PDCCH is transmitted. A plurality of
downlink CCs correspond to respective bits of the monitoring set
field, and the downlink CC on which the PDCCH is transmitted may be
expressed by `1`. For example, in case of FIG. 20, the monitoring
set field may have a size of 3 bits. In the subframe n, the
monitoring set field for the UE #1 may be 111. In the subframe n+1,
the monitoring set field for the UE #1 may be 010. In the subframe
n+k, the monitoring set field for the UE #1 may be 101.
[0139] In FIG. 19 and FIG. 20, the PDCCH map is dynamically
transmitted in every subframe. In this case, the downlink CC on
which the PDCCH is transmitted changes dynamically in every
subframe.
[0140] The BS may configure the PDCCH map semi-statically via
higher layer signaling such as RRC. In this case, the downlink CC
on which the PDCCH is transmitted changes semi-statically.
[0141] FIG. 21 shows an example of semi-statically configured a
PDCCH map.
[0142] Referring to FIG. 21, a multi-carrier system uses three
downlink CCs, i.e., CC #1, CC #2, and CC #3. The PDCCH map includes
a monitoring set field. It is assumed that a monitoring field set
for the UE #1 indicates the CC #1 and the CC #3 and does not
indicate the CC #2. The PDCCH map is semi-statically configured,
and thus the PDCCH for the UE #1 is transmitted only through the CC
#1 and the CC #3 from a subframe n to a subframe n+k. In FIG. 21, a
PDSCH corresponding to the PDCCH is transmitted only through a
downlink CC on which the PDCCH is transmitted. That is, if the
PDCCH is transmitted through the CC #1, the PDSCH corresponding to
the PDCCH is transmitted only through the CC #1. In this case, the
PDSCH for the UE #1 cannot be transmitted through the CC #2.
Therefore, the UE #1 may not receive any information in the CC #2.
If the BS intends to transmit small-sized downlink data to the UE
#1 through the PDSCH, there is no problem even if the CC #2 is not
used for transmission of downlink data for the UE #1.
[0143] If a radio resource scheduling scheme is a semi-persistent
scheduling (SPS) scheme, the UE can read downlink data on the PDSCH
without having to receive the PDCCH. Therefore, the BS can transmit
the PDSCH based on the SPS scheme through the CC #2.
[0144] FIG. 22 shows another example of semi-statically configured
a PDCCH map. In FIG. 22, similarly to FIG. 21, a multi-carrier
system uses three downlink CCs, i.e., CC #1, CC #2, and CC #3. It
is assumed that a monitoring field set for the UE #1 is included in
the PDCCH map, and indicates the CC #1 and the CC #3 and does not
indicate the CC #2.
[0145] Referring to FIG. 22, a downlink CC on which a PDSCH is
transmitted may be equal to or different from a downlink CC on
which a PDCCH for scheduling the PDSCH is transmitted. Therefore, a
PDCCH for the UE #1 is transmitted only through the CC #1 and the
CC #3 indicated by the monitoring set field, whereas the PDSCH may
be transmitted through all downlink CCs, i.e., the CC #1 to the CC
#3. In a subframe n+1, a PDCCH for the CC #2 is transmitted through
the CC #1. In this case, according to a CC indicator or a
predetermined rule, the UE #1 can know for which downlink CC the
PDCCH is used.
[0146] If L CCs can be constructed for one LTE-A UE, only A CCs out
of the L CCs can be used (L.gtoreq.N, where L and N are natural
numbers). An active CC set is a CC set having the A CCs out of the
L CCs as its elements. The aforementioned monitoring set field can
be used in the active CC set defined with the A CCs.
[0147] Next, the CCE field is described.
[0148] A UE has to attempt blind decoding for each CCE aggregation
level. Therefore, a blind decoding complexity can be significantly
decreased if the CCE aggregation level to be monitored by the UE is
limited. If a wireless communication system uses X CCE aggregation
levels, a BS can transmit a PDCCH to the UE by using Y CCE
aggregation levels (X.gtoreq.Y, where X and Y are natural numbers).
In this case, when the BS reports information regarding the Y CCE
aggregation levels to the UE, the UE performs blind decoding only
for the Y CCE aggregation levels. Accordingly, the blind decoding
complexity of the UE can be decreased. That is, the CCE field
indicates the Y CCE aggregation levels out of the X CCE aggregation
levels. The UE can monitor a PDCCH only for each of the Y CCE
aggregation levels indicated by the CCE field. The Y CCE
aggregation levels indicated by the CCE field will be referred
hereinafter as a subset level.
[0149] For example, if the wireless communication system uses 4 CCE
aggregation levels, such as, {1, 2, 4, 8}, the subset level can be
indicated according to a CCE field value as described in the
following table.
TABLE-US-00004 TABLE 4 CCE field Subset level 0 {1, 2, 4, 8} 1 {1,
2, 4} 2 {2, 4, 8} 3 {4, 8}
[0150] Table 4 is for exemplary purposes only, and thus the subset
level can be variously configured according to the CCE field value.
The CCE field may indicate a different subset level for each a DCI
format or a DCI format group. Alternatively, the CCE field may
indicate a subset level only for a specific DCI format by using the
CCE field. In addition, the CCE field may indicate a different
subset level for each a downlink CC or a downlink CC group.
[0151] The CCE field may be included in a PDCCH map. Therefore, the
aforementioned description on the PDCCH map can be equally applied
to the CCE field. The CCE field can be transmitted dynamically or
semi-statically.
[0152] As such, the CCE aggregation level may be explicitly limited
to the subset level by using the CCE field. Alternatively, the CCE
aggregation level may be implicitly limited to the subset level.
For example, all PDCCHs in a subframe may be specified to use the
same CCE aggregation level. If the UE finds one PDCCH from a
plurality of PDCCHs at one CCE aggregation level, the UE monitors
the remaining PDCCHs also at the CCE aggregation level.
[0153] FIG. 23 shows a control channel monitoring method performed
by a UE in a multi-carrier system.
[0154] Referring to FIG. 23, three PDCCHs, i.e., PDCCH #1, PDCCH
#2, and PDCCH #3, for a UE #1 are allocated to logically contiguous
CCEs on a CCE aggregation.
[0155] As such, a BS can transmit a plurality of PDCCHs for one UE
through one downlink CC. The plurality of PDCCHs can have
independent CCE aggregation levels. The plurality of PDCCHs can be
allocated to logically contiguous CCEs. If the UE detects the PDCCH
#2, a CCE index (4 to 7) of a CCE aggregation on which the PDCCH #2
is transmitted can be used to facilitate detection of another PDCCH
from CCEs located in a front or rear portion in the CCE
aggregation.
[0156] FIG. 24 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.
[0157] 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.
[0158] Accordingly, a reception complexity of a PDCCH in the UE can
be decreased in a multi-carrier system. A method and an apparatus
of effectively monitoring a PDCCH are provided. As a result, power
consumption of the UE can be decreased. Therefore, overall system
performance can be improved.
[0159] 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.
[0160] 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.
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