METHOD AND APPARATUS OF RECEIVING DATA IN WIRELESS COMMUNICATION SYSTEM

Info

Publication number: 20110194514
Type: Application
Filed: Jul 30, 2009
Publication Date: Aug 11, 2011
Inventors: Moon Il Lee (Gyeongki-do), Seung Hee Han (Gyeongki-do), Hyun Soo Ko (Gyeongki-do), Jae Hoon Chung (Gyeongki-do), So Yeon Kim (Gyeongki-do)
Application Number: 13/056,460

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.

Description

Description

TECHNICAL FIELD

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

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.

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.

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.

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.

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.

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

The present invention provides a method and an apparatus of receiving data in a wireless communication system.

Solution to Problem

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.

Preferably, the DL grant comprises a CC indication field indicating the second DL CC.

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.

Preferably, an index of a control channel element (CCE) indicates the second DL CC, the CCE is used for transmitting the PDCCH.

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.

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.

Preferably, the UL grant comprises a CC indication field indicating the first UL CC.

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.

Preferably, the DL grant comprises a CC indication field indicating the second DL CC.

Advantageous Effects of Invention

A method and an apparatus of effectively receiving data are provided. Accordingly, overall system performance can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a wireless communication system.

FIG. 2 shows an example of a plurality of component carriers (CCs) used in a multi-carrier system.

FIG. 3 is a block diagram showing an example of a multi-carrier system.

FIG. 4 shows an example of a plurality of physical channels (PHYs).

FIG. 5 shows an example of a bandwidth used by a PHY.

FIG. 6 shows an example of an asymmetric structure of downlink and uplink in a multi-carrier system.

FIG. 7 shows a structure of a radio frame.

FIG. 8 shows an example of a resource grid for one downlink slot.

FIG. 9 shows a structure of a radio frame and a subframe in a frequency division duplex (FDD) system.

FIG. 10 shows an example of an resource element group (REG) structure when a base station (BS) uses one or two transmit (Tx) antennas.

FIG. 11 shows an example of an REG structure when a BS uses four Tx antennas.

FIG. 12 shows an example of mapping of a physical control format indicator channel (PCFICH) to REGs.

FIG. 13 is a flow diagram showing an example of a method of transmitting data and receiving data performed by a user equipment (UE).

FIG. 14 is a flowchart showing an example of a method of configuring a physical downlink control channel (PDCCH).

FIG. 15 shows an example of a method of multiplexing a plurality of PDCCHs for a plurality of UEs, performed by a BS.

FIG. 16 shows an example of a method of monitoring a control channel, performed by a UE.

FIG. 17 shows an example of a PDCCH transmission method in a multi-carrier system.

FIG. 18 is a flow diagram showing method of receiving data, performed by a UE, according to an embodiment of the present invention.

FIG. 19 is a flow diagram showing method of transmitting data, performed by a UE, according to another embodiment of the present invention.

FIG. 20 illustrates a method of configuring a multi-PDCCH.

FIG. 21 shows an example in which a multi-PDCCH is transmitted in a multi-carrier system.

FIG. 22 shows another example in which a multi-PDCCH is transmitted in a multi-carrier system.

FIG. 23 shows still another example in which a multi-PDCCH is transmitted in a multi-carrier system.

FIG. 24 shows an example in which PDCCHs are transmitted in a multi-carrier system.

MODE FOR THE INVENTION

FIG. 1 is a block diagram showing a wireless communication system.

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.

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.

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.

If the transmitter and the receiver use multi-antenna, the wireless communication system may be called as multiple input multiple output (MIMO) system.

FIG. 2 shows an example of a plurality of component carriers (CCs) used in a multi-carrier system.

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

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.

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.

FIG. 3 is a block diagram showing an example of a multi-carrier system.

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.

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.

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.

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.

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).

Referring to FIG. 4, each of M PHYs has a specific bandwidth (BW). An PHY #m has a center frequency f_c,mand a bandwidth of N_IFFT,m×Δf_m(where m=1, . . . , M). Herein, N_IFFT,mdenotes an inverse fast Fourier transform (IFFT) size of the PHY #m, and Δf_mdenotes 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.

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.

FIG. 5 shows an example of a bandwidth used by a PHY.

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.

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≧L, where M and L are natural numbers). Herein, L may differ depending on a type of the UE.

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.

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.

Hereinafter, for convenience of explanation, it is assumed that a CC includes one PHY.

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.

Now, a single carrier system will be described.

FIG. 7 shows a structure of a radio frame.

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.

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.

FIG. 8 shows an example of a resource grid for one downlink slot.

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^DLof 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.

Each element on the resource grid is referred to as a resource element (RE). Although it is described herein that one RB includes 7×12 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.

The resource grid for one downlink slot of FIG. 8 can be applied to a resource grid for an uplink slot.

FIG. 9 shows a structure of a radio frame and a subframe in a FDD system.

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.

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.

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.

Resource element groups (REGs) are used for defining the mapping of a control channel to resource elements.

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.

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 (pε{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.

The PHICH carries an HARQ acknowledgement (ACK)/not-acknowledgement (NACK) for uplink data.

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.

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.

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 1

TABLE 1 CFI codeword CFI <b₀, b₁, . . . , b₃₁> 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>

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.

FIG. 12 shows an example of mapping of a PCFICH to REGs.

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.

Now, a PDCCH will be described.

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}.

The following table shows an example of the PDCCH format, the number of REGs and the number of PDCCH bits.

Table 2

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

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.

FIG. 13 is a flow diagram showing an example of a method of transmitting data and receiving data performed by a UE.

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.

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.

As described above, a UE shall receive DCI on PDCCH to receive downlink data from a BS or transmit uplink data to a BS.

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.

The following table shows an example of the DCI format.

Table 3

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

Referring to above table, a DCI format 0 is used for PUSCH scheduling. The DCI format 0 is used for an uplink grant.

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.

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.

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.

FIG. 14 is a flowchart showing an example of a method of configuring a PDCCH.

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.

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.

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.

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.

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.

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.

FIG. 15 shows an example of a method of multiplexing a plurality of PDCCHs for a plurality of UEs, performed by a BS.

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.

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.

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.

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.

FIG. 16 shows an example of a method of monitoring a control channel, performed by a UE.

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.

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.

FIG. 17 shows an example of a PDCCH transmission method in a multi-carrier system.

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.

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.

In a type 3, the BS uses an independent PDCCH in each of several DL CCs. A

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.

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.

FIG. 18 is a flow diagram showing method of receiving data, performed by a UE, according to an embodiment of the present invention.

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).

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.

FIG. 19 is a flow diagram showing method of transmitting data, performed by a UE, according to another embodiment of the present invention.

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).

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.

(1) Method of Adding a CC Indication Bit Field (CIBF) when Generating an Information Bit Stream

A CIBF can be added to each DCI format as an information field.

The following table lists examples of CCs indicated by respective CIBF according to respective CIBF values.

Table 4

TABLE 4 CIBF CARRIER NUMBER 00 CC #1 01 CC #2 10 CC #3 11 CC #4

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.

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.

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.

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.

(2) Method of Masking Carrier Information to CRC

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.

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.

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.

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≧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.

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.

(3) Method of Implicitly Indicating Carrier Information

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.

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.

(4) Method of Transmitting Carrier Information Through RRC Signaling

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.

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.

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.

FIG. 20 illustrates a method of configuring a multi-PDCCH.

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.

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.

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.

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.

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.

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.

FIG. 21 shows an example in which a multi-PDCCH is transmitted in a multi-carrier system.

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.

FIG. 22 shows another example in which a multi-PDCCH is transmitted in a multi-carrier system.

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.

A CC through which a multi-PDCCH is transmitted is described below.

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.

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.

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.

FIG. 23 shows still another example in which a multi-PDCCH is transmitted in a multi-carrier system.

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.

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.

FIG. 24 shows an example in which PDCCHs are transmitted in a multi-carrier system.

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.

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.

FIG. 25 shows an example in which CC subsets are set.

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.

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.

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.

It is hereinafter assumed that a UE uses a CC subset and a PDCCH includes a CIBF.

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.

Although DL CCs have so far been described, UL CCs may also be limited to a CC subset.

The length of a CP in each CC is described below.

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.

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.

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.

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.

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.

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.

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.