# Patent

## Title
Method and device for reporting channel state information in wireless communication system

## Abstract

A method is described for a user equipment (UE) to report channel state information (CSI) including at least one of a rank indicator (RI), a precoding matrix indicator (PMI) or a channel quality indicator (CQI) in a wireless communication system. The UE reports the RI to an evolved Node B (eNB), drops a report of the PMI after reporting the RI to the eNB, and reports the CQI to the eNB after dropping the PMI report. A rank value corresponding to the RI is changed from a rank value corresponding to a most recently reported RI before reporting the RI to the eNB. The CQI is determined based on the RI and a precoding matrix that does not correspond to the dropped PMI report.

## Background
This application is the National Phase of PCT/KR2012/007943 filed on Sep. 28, 2012, which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/540,532 filed on Sep. 28, 2011, all of which are hereby expressly by reference into the present application.


TECHNICAL FIELD
The following description relates to a wireless communication system and, more particularly, to a method and device for reporting channel state information (CSI).
BACKGROUND ART
MIMO (multiple-input multiple-output) refers to a method for improving transmission/reception efficiency by adopting multiple transmit (Tx) antennas and multiple receive (Rx) antennas instead of a single Tx antenna and a single Rx antenna. That is, MIMO is a technology for increasing capacity or improving performance by using multiple antennas at a transmitting end or a receiving end of a wireless communication system. MIMO may be referred to as multi-antenna technology. To correctly perform multi-antenna transmission, it is necessary to feed back information on a channel from a receiving end that receives multiple antenna channels.
A rank indicator (RI), a precoding matrix index (PMI), a channel quality indicator (CQI), etc. are defined as information fed back from a receiving end to a transmitting end in a conventional multi-antenna wireless communication system. The RI, PMI and CQI are commonly referred to as channel state information (CSI). The CSI is configured to be suitable for multi-antenna transmission. In general, the RI may be determined as a value indicating a most suitable rank in the current channel state, the PMI may be determined as a value indicating a most suitable precoding matrix based on the rank and the CQI may be determined as a value indicating a most suitable modulation and coding scheme (MCS) based on the RI and PMI.
DISCLOSURE
Technical Problem
Specific CSI may be dropped due to collision with another CSI during CSI reporting. For example, when a PMI report is dropped, it may be difficult to calculate/determine the CQI since CQI calculation/determination is performed based on the PMI.
An object of the present invention devised to solve the problem lies in a method for correctly and efficiently calculating/determining CSI reported after a CSI report is dropped.
The technical problems solved by the present invention are not limited to the above technical problems and those skilled in the art may understand other technical problems from the following description.
Technical Solution
The object of the present invention can be achieved by providing a method for a user equipment (UE) to report channel state information (CSI) in a wireless communication system, including: reporting a rank indicator (RI); dropping a report of a precoding matrix indicator (PMI) after reporting the RI; and reporting a channel quality indicator (CQI) after dropping the PMI. A rank value corresponding to the RI is changed from a rank value corresponding to the most recently reported RI before reporting the RI. The CQI is determined on the basis of a precoding matrix other than a precoding matrix corresponding to the dropped PMI.
In another embodiment of the present invention, provided herein is a UE for reporting CSI in a wireless communication system, including: a reception module for reporting a downlink signal from an eNB; a transmission module for transmitting an uplink signal to the eNB; and a processor for controlling the UE comprising the reception mode and the transmission module. The processor is configured to report a rank indicator (RI); to drop a report of a precoding matrix indicator (PMI) after reporting the RI; and to report a channel quality indicator (CQI) after dropping the PMI. A rank value corresponding to the RI is changed from a rank value corresponding to the most recently reported RI before reporting the RI. The CQI is determined on the basis of a precoding matrix other than a precoding matrix corresponding to the dropped PMI.
The following may be commonly applied to the above-described embodiments of the present invention.
The CQI may be determined on the basis of a precoding matrix corresponding to a PMI having the lowest index, selected from a codebook corresponding to the changed rank value.
The PMI having the lowest index may be determined in a restricted codebook subset.
The CQI may be determined on the basis of the changed rank value and a precoding matrix corresponding to the most recently reported PMI from among PMIs reported before reporting the RI.
The CQI may be determined on the basis of a precoding matrix corresponding to the most recently reported PMI from among PMIs reported before reporting the RI and a rank value corresponding to the most recently reported PMI.
The method may further include reporting the dropped PMI after dropping the PMI and before reporting the CQI.
The dropped PMI may be reported at the next reporting opportunity determined according to a CSI reporting period.
The dropped PMI may be reported in a subframe subsequent to a subframe in which the PMI report is dropped.
The dropping of the PMI may be performed when the PMI and other CSI collide.
The other CSI may be CSI having high priority from among CSI of another cell.
CSI reporting may include reporting the RI, wideband PMI and wideband CQI, and subband CQI.
The CSI may be reported through a physical uplink control channel (PUCCH).
The CSI may be periodically reported.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Advantageous Effects
According to the present invention, it is possible to efficiently transmit information in a wireless communication system. In addition, it is possible to provide a method and device for correctly and efficiently calculating/determining CSI reported after a CSI report is dropped.
The effects of the present invention are not limited to the above-described effects and other effects which are not described herein will become apparent to those skilled in the art from the following description.



DESCRIPTION OF DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:
FIG. 1 illustrates a radio frame structure;
FIG. 2 illustrates a resource grid in a downlink slot;
FIG. 3 illustrates a downlink subframe structure;
FIG. 4 illustrates an uplink subframe structure;
FIG. 5 illustrates configurations of a physical layer (L1) and a MAC layer (L2) of a multi-carrier supporting system;
FIG. 6 conceptually illustrates component carriers (CCs) for downlink and uplink;
FIG. 7 illustrates exemplary DL/UL CC linkage;
FIG. 8 illustrates an SC-FDMA transmission scheme and OFDMA transmission scheme;
FIG. 9 illustrates maximum Tx power in case of single antenna transmission and multi-antenna transmission;
FIG. 10 illustrates a configuration of a MIMO system;
FIG. 11 illustrates a CDD structure in a MIMO system;
FIG. 12 illustrates codebook based precoding;
FIG. 13 illustrates a resource mapping structure of a PUCCH;
FIG. 14 illustrates channel structures of CQI information bits;
FIG. 15 illustrates CQI and ACK/NACK information transmission;
FIG. 16 illustrates CSI feedback;
FIG. 17 illustrates an exemplary CQI report mode;
FIG. 18 illustrates a method for periodically transmitting channel information by a UE;
FIG. 19 illustrates SB CQI transmission;
FIG. 20 illustrates WB CQI and SB CQI transmission;
FIG. 21 illustrates WB CQI, SB CQI and RI transmission;
FIG. 22 illustrates exemplary control information transmission timing in PUCCH report mode 2-1;
FIG. 23 illustrates exemplary CSI reporting to which the present invention is applicable;
FIG. 24 illustrates dropped PMI reporting timing according to an embodiment of the present invention;
FIG. 25 illustrates a method for reporting CSI according to an embodiment of the present invention; and
FIG. 26 illustrates a configuration of a transceiver according to an embodiment of the present invention.



BEST MODE 
The embodiments of the present invention described hereinbelow are combinations of elements and features of the present invention. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment.
In the embodiments of the present invention, a description is made, centering on a data transmission and reception relationship between a base station (BS) and a user equipment (UE). The BS is a terminal node of a network, which communicates directly with a UE. In some cases, a specific operation described as performed by the BS may be performed by an upper node of the BS.
Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with a UE may be performed by the BS, or network nodes other than the BS. The term ‘BS’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point (AP)’, etc. The term ‘UE’ may be replaced with the term ‘terminal’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’, ‘Subscriber Station (SS)’, etc.
Specific terms used for the embodiments of the present invention are provided to help the understanding of the present invention. These specific terms may be replaced with other terms within the scope and spirit of the present invention.
In some cases, to prevent the concept of the present invention from being ambiguous, structures and apparatuses of the known art will be omitted, or will be shown in the form of a block diagram based on main functions of each structure and apparatus. Also, wherever possible, the same reference numbers will be used throughout the drawings and the specification to refer to the same or like parts.
The embodiments of the present invention can be supported by standard documents disclosed for at least one of wireless access systems, Institute of Electrical and Electronics Engineers (IEEE) 802, 3rd Generation Partnership Project (3GPP), 3GPP Long Term Evolution (3GPP LTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are not described to clarify the technical features of the present invention can be supported by those documents. Further, all terms as set forth herein can be explained by the standard documents.
Techniques described herein can be used in various wireless access systems such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-Frequency Division Multiple Access (SC-FDMA), etc. CDMA may be implemented as a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented as a radio technology such as Global System for Mobile communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a part of Universal Mobile Telecommunication System (UMTS). 3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA for downlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (Wireless Metropolitan Area Network (WirelessMAN-OFDMA Reference System) and the IEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity, this application focuses on the 3GPP LTE/LTE-A system. However, the technical features of the present invention are not limited thereto.
A description will be given of a downlink radio frame structure with reference to FIG. 1.
In a cellular OFDM wireless packet communication system, uplink/downlink data packet transmission is performed on a subframe-by-subframe basis and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. 3GPP LTE supports type-1 radio frame applicable to FDD (frequency division duplex) and type-2 radio frame applicable to TDD (time division duplex).
FIG. 1(a) illustrates a type-1 radio frame structure. A downlink radio frame includes 10 subframes. Each subframe is further divided into two slots in the time domain. A unit time during which one subframe is transmitted is defined as transmission time interval (TTI). For example, one subframe may be 1 ms in duration and one slot may be 0.5 ms in duration. A slot may include a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. Since 3GPP LTE adopts OFDMA for downlink, an OFDM symbol represents one symbol period. An OFDM symbol may be referred to as an SC-FDMA symbol or symbol period. A resource block (RB) is a resource allocation unit including a plurality of contiguous subcarriers in a slot.
The number of OFDM symbols included in one slot may depend on cyclic prefix (CP) configuration. CPs include an extended CP and a normal CP. When an OFDM symbol is configured with the normal CP, for example, the number of OFDM symbols included in one slot may be 7. When an OFDM symbol is configured with the extended CP, the duration of one OFDM symbol increases, and thus the number of OFDM symbols included in one slot is smaller than that in case of the normal CP. In case of the extended CP, the number of OFDM symbols allocated to one slot may be 6. When a channel state is unstable, such as a case in which a UE moves at a high speed, the extended CP can be used to reduce inter-symbol interference.
When the normal CP is used, one subframe includes 14 OFDM symbols since one slot has 7 OFDM symbols. The first two or three OFDM symbols in each subframe can be allocated to a PDCCH and the remaining OFDM symbols can be allocated to a PDSCH.
FIG. 1(b) illustrates a type-2 radio frame structure. The type-2 radio frame includes 2 half frames. Each half frame includes 5 subframes, a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS). One subframe consists of 2 slots. The DwPTS is used for initial cell search, synchronization or channel estimation in a UE. The UpPTS is used for channel estimation in a BS and UL transmission synchronization acquisition in a UE. The GP eliminates UL interference caused by multi-path delay of a DL signal between a UL and a DL. One subframe includes 2 slots irrespective of radio frame type. This radio frame structure is purely exemplary and thus the number of subframes in a radio frame, the number of slots in a subframe, or the number of OFDM symbols in a slot may vary.
FIG. 2 illustrates a resource grid in a downlink slot. While one downlink slot includes 7 OFDM symbols in the time domain and one RB includes 12 subcarriers in the frequency domain in FIG. 2, the present invention is not limited thereto. For example, one slot includes 7 OFDM symbols in the case of normal CP whereas one slot includes 6 OFDM symbols in the case of extended CP. Each element on the resource grid is referred to as a resource element (RE). One RB includes 12×7(6) REs. The number NDL of RBs included in the downlink slot depends on a downlink transmit bandwidth. The structure of an uplink slot may be same as that of the downlink slot.
FIG. 3 illustrates a downlink subframe structure. A maximum of three OFDM symbols located in a front portion of a first slot within a subframe correspond to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to a data region to which a physical downlink shared chancel (PDSCH) is allocated. Examples of downlink control channels used in 3GPP LTE include a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used for transmission of control channels within the subframe. The PHICH is a response of uplink transmission and carries an HARQ acknowledgment (ACK)/negative-acknowledgment (NACK) signal. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information or uplink Tx power control commands for an arbitrary UE group. The PDCCH may carry a transport format and a resource allocation of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, information on resource allocation of an upper-layer control message such as a random access response transmitted on the PDSCH, a set of Tx power control commands on individual UEs within an arbitrary UE group, a Tx power control command, information on activation of a voice over IP (VoIP), etc. A plurality of PDCCHs can be transmitted within a control region. The UE can monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel. The CCE corresponds to a plurality of resource element groups (REGs). A format of the PDCCH and the number of bits of the available PDCCH are determined by the number of CCEs. The BS determines a PDCCH format according to DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to control information. The CRC is masked with an identifier referred to as a radio network temporary identifier (RNTI) according to an owner or usage of the PDCCH. If the PDCCH is for a specific UE, a cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively, when the PDCCH is for a paging message, a paging indicator identifier (P-RNTI) may be masked to the CRC. When the PDCCH is for system information (more specifically, a system information block (SIB)), a system information identifier and system information RNTI (SI-RNTI) may be masked to the CRC. To indicate a random access response corresponding to a response to transmission of a random access preamble of the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC.
FIG. 4 illustrates an uplink subframe structure. An uplink subframe may be divided into a control region and a data region in the frequency domain. The control region is allocated a PUCCH including uplink control information. The data region is allocated a PUSCH including user data. To maintain single carrier property, one UE cannot simultaneously transmit a PUCCH and a PUSCH. A PUCCH for a UE is allocated to an RB pair. RBs belonging to an RB pair occupy different subcarriers in 2 slots. That is, an RB pair allocated to a PUCCH is frequency-hopped at a slot boundary.
Carrier Aggregation
Although downlink and uplink bandwidths are different from each other, a wireless communication system typically uses one carrier. For example, a wireless communication system having one carrier for each of the downlink and the uplink and symmetry between the downlink and uplink bandwidths may be provided based on a single carrier.
The International Telecommunication Union (ITU) requests that IMT-Advanced candidates support wider bandwidths, compared to legacy wireless communication systems. However, allocation of a wide frequency bandwidth is difficult throughout most of the world. Accordingly, a technology for efficiently using small segmented bands, known as carrier aggregation (bandwidth aggregation) or spectrum aggregation, has been developed in order to aggregate a plurality of physical bands to a wider logical band.
Carrier aggregation was introduced to support increased throughput, prevent cost increase caused by introduction of wideband RF devices, and ensure compatibility with legacy systems. Carrier aggregation enables data exchange between a UE and a BS through a group of carriers each having a bandwidth unit defined in a legacy wireless communication system (e.g. 3GPP LTE Release-8 or Release-9 in case of 3GPP LTE-A). The carriers each having a bandwidth unit defined in the legacy wireless communication system may be called Component Carriers (CCs). Carrier aggregation using one or more CCs may be applied to each of downlink and uplink. Carrier aggregation may support a system bandwidth of up to 100 MHz by aggregating up to five CCs each having a bandwidth of 5, 10 or 20 MHz.
A downlink CC and an uplink CC may be represented as a DL CC and a UL CC, respectively. A carrier or CC may be represented as a cell in terms of function in the 3GPP LTE system. Thus, a DL CC and a UL CC may be referred to as a DL cell and a UL cell, respectively. Hereinbelow, the terms ‘carriers’, ‘component carriers’, ‘CCs’ or ‘cells’ will be used to signify a plurality of carriers to which carrier aggregation is applied.
While the following description exemplarily uses a BS (or cell) as a downlink transmission entity and exemplarily uses a UE as an uplink transmission entity, the scope or spirit of the present invention is not limited thereto. That is, even when a relay node (RN) may be used as a downlink transmission entity from a BS to a UE and or be used as an uplink reception entity from a UE to a BS, or even when the RN may be used an uplink transmission entity for a UE or be used as a downlink reception entity from a BS, it should be noted that the embodiments of the present invention can be applied without difficulty.
Downlink carrier aggregation may be described as a BS supporting downlink transmission to a UE in frequency resources (subcarriers or physical resource blocks [PRBs]) of one or more carrier bands in time resources (allocated in units of a subframe). Uplink carrier aggregation may be described as a UE supporting uplink transmission to a BS in frequency resources (subcarriers or PRBs) of one or more carrier bands in time resources (allocated in units of a subframe).
FIG. 5 shows a physical layer (first layer, L1) and a MAC layer (second layer, L2) of a multi-carrier supporting system. A BS of the legacy wireless communication system supporting a single carrier includes one physical layer (PHY) entity capable of supporting one carrier, and one medium access control (MAC) entity for controlling one PHY entity may be provided to the BS. For example, baseband processing may be carried out in the PHY layer. For example, the L1/L2 scheduler operation including not only MAC PDU (Protocol Data Unit) creation of a transmitter but also MAC/RLC sub-layers may be carried out in the MAC layer. The MAC PDU packet block of the MAC layer is converted into a transport block through a logical transport layer, such that the resultant transport block is mapped to a physical layer input information block. In FIG. 5, the MAC layer is represented as the entire L2 layer, and may conceptually cover MAC/RLC/PDCP sub-layers. For convenience of description and better understanding of the present invention, the above-mentioned application may be used interchangeably in the MAC layer description of the present invention.
On the other hand, a multicarrier-supporting system may provide a plurality of MAC-PHY entities. In more detail, as can be seen from FIG. 5(a), the transmitter and receiver of the multicarrier-supporting system may be configured in such a manner that one MAC-PHY entity is mapped to each of n component carriers (n CCs). An independent PHY layer and an independent MAC layer are assigned to each CC, such that a PDSCH for each CC may be created in the range from the MAC PDU to the PHY layer.
Alternatively, the multicarrier-supporting system may provide one common MAC entity and a plurality of PHY entities. That is, as shown in FIG. 5(b), the multicarrier-supporting system may include the transmitter and the receiver in such a manner that n PHY entities respectively correspond to n CCs and one common MAC entity controlling the n PHY entities may be present in each of the transmitter and the receiver. In this case, a MAC PDU from one MAC layer may be branched into a plurality of transport blocks corresponding to a plurality of CCs through a transport layer. Alternatively, when generating a MAC PDU in the MAC layer or when generating an RLC PDU in the RLC layer, the MAC PDU or RLC PDU may be branched into individual CCs. As a result, a PDSCH per CC may be generated in the PHY layer.
PDCCH for transmitting L1/L2 control signaling control information generated from a packet scheduler of the MAC layer may be mapped to physical resources for each CC, and then transmitted. In this case, PDCCH that includes control information (DL assignment or UL grant) for transmitting PDSCH or PUSCH to a specific UE may be separately encoded at every CC carrying the corresponding PDSCH/PUSCH. The PDCCH may be called a separate coded PDCCH. On the other hand, PDSCH/PUSCH transmission control information of several CCs may be configured in one PDCCH such that the configured PDCCH may be transmitted. This PDCCH may be called a joint coded PDCCH.
To support carrier aggregation, connection between a BS and a UE (or RN) needs to be established and preparation of connection setup between the BS and the UE is needed in such a manner that a control channel (PDCCH or PUCCH) and/or a shared channel (PDSCH or PUSCH) can be transmitted. In order to perform the above-mentioned connection or connection setup for a specific UE or RN, measurement and/or reporting for each carrier are needed, and CCs serving as the measurement and/or reporting targets may be assigned. In other words, CC assignment means that CCs (indicating the number of CCs and indexes of CCs) used for DL/UL transmission are established in consideration of not only capabilities of a specific UE (or RN) from among UL/DL CCs constructed in the BS but also system environment.
In this case, when CC assignment is controlled in third layer (L3) Radio Resource Management (RRM), UE-specific or RN-specific RRC signaling may be used. Alternatively, cell-specific or cell cluster-specific RRC signaling may be used. Provided that dynamic control such as a series of CC activation/deactivation settings is needed for CC assignment, a predetermined PDCCH may be used for L1/L2 control signaling, or a dedicated physical control channel for CC assignment control information or an L2 MAC-message formatted PDSCH may be used. On the other hand, if CC assignment is controlled by a packet scheduler, a predetermined PDCCH may be used for L1/L2 control signaling, a physical control channel dedicated for CC assignment control information may be used, or a PDSCH configured in the form of an L2 MAC message may be used.
FIG. 6 is a conceptual diagram illustrating downlink (DL) and uplink (UL) component carriers (CCs). Referring to FIG. 6, DL and UL CCs may be assigned from a BS (cell) or RN. For example, the number of DL CCs may be set to N and the number of UL CCs may be set to M.
Through initial access or initial deployment process of a UE, after RRC connection is established on the basis of one certain CC for DL or UL (cell search) (for example, system information acquisition/reception, initial random access process, etc.), a unique carrier setup for each UE may be provided from a dedicated signaling (UE-specific RRC signaling or UE-specific L1/L2 PDCCH signaling). For example, assuming that a carrier setup for UE is commonly achieved in units of a BS (cell or cell-cluster), the UE carrier setup may also be provided through cell-specific RRC signaling or cell-specific UE-common L1/L2 PDCCH signaling. In another example, carrier component information for use in a BS may be signaled to a UE through system information for RRC connection setup, or may also be signaled to additional system information or cell-specific RRC signaling upon completion of the RRC connection setup.
While DL/UL CC setup has been described, centering on the relationship between a BS and a UE, to which the present invention is not limited, an RN may also provide DL/UL CC setup to a UE contained in an RN region. In addition, in association with an RN contained in a BS region, the BS may also provide DL/UL CC setup of the corresponding RN to the RN of the BS region. For clarity, while the following description will disclose DL/UL CC setup on the basis of the relationship between the BS and the UE, it should be noted that the same content may also be applied to the relationship between the RN and the UE (i.e., access uplink and downlink) or the relation between the BS and the RN (backhaul uplink or downlink) without departing from the scope or spirit of the present invention.
When the above-mentioned DL/UL CCs are uniquely assigned to individual UEs, DL/UL CC linkage may be implicitly or explicitly configured through a certain signaling parameter definition.
FIG. 7 shows an exemplary linkage of DL/UL CCs. In more detail, when a BS configures two DL CCs (DL CC #a and DL CC #b) and two UL CCs (UL CC #i and UL CC #j), FIG. 7 shows a DL/UL CC linkage defined when two DL CCs (DL CC #a and DL CC #b) and one UL CC (UL CC #i) are assigned to a certain UE. In a DL/UL CC linkage setup shown in FIG. 7, a solid line indicates a linkage setup between DL CC and UL CC that are basically constructed by a BS, and this linkage setup between DL CC and UL CC may be defined in “System Information Block (SIB) 2”. In the DL/UL CC linkage setup shown in FIG. 7, a dotted line indicates a linkage setup between DL CC and UL CC configured in a specific UE. The above-mentioned DL CC and UL CC linkage setup shown in FIG. 7 is disclosed only for illustrative purposes, and the scope or spirit of the present invention is not limited thereto. That is, in accordance with various embodiments of the present invention, the number of DL CCs or UL CCs configured by a BS may be set to an arbitrary number. Thus, the number of UE-specific DL CCs or the number of UE-specific UL CCs in the above-mentioned DL CCs or UL CCs may be set to an arbitrary number, and associated DL/UL CC linkage may be defined in a different way from that of FIG. 7.
Further, from among DL CCs and UL CCs configured or assigned, a primary CC (PCC), or a primary cell (P-cell) or an anchor CC (also called an anchor cell) may be configured. For example, a DL PCC (or DL P-cell) aiming to transmit configuration/reconfiguration information on RRC connection setup may be configured. In another example, UL CC for transmitting PUCCH to be used when a certain UE transmits UCI that must be transmitted on uplink may be configured as UL PCC (or UL P-cell). For convenience of description, it is assumed that one DL PCC (P-cell) and one UL PCC (P-cell) are basically assigned to each UE. Alternatively, if a large number of CCs is assigned to UE or if CCs can be assigned from a plurality of BSs, one or more DL PCCs (P-cells) and/or one or more UL PCCs (P-cells) may be assigned from one or more BSs to a certain UE. For linkage between DL PCC (P-cell) and UL PCC (P-cell), a UE-specific configuration method may be considered by the BS as necessary. To implement a more simplified method, a linkage between DL PCC (P-cell) and UL PCC (P-cell) may be configured on the basis of the relationship of basic linkage that has been defined in LTE Release-8 (LTE Rel-8) and signaled to System Information Block (or Base) 2. DL PCC (P-cell) and UL PCC (P-cell) for the above-mentioned linkage configuration are grouped so that the grouped result may be denoted by a UE-specific P-cell.
SC-FDMA Transmission and OFDMA Transmission
FIG. 8 is a conceptual diagram illustrating an SC-FDMA transmission scheme and an OFDMA transmission scheme for use in a mobile communication system. The SC-FDMA transmission scheme may be used for UL transmission and the OFDMA transmission scheme may be used for DL transmission.
Each of the UL signal transmission entity (e.g., UE) and the DL signal transmission entity (e.g., BS) may include a serial-to-parallel (S/P) Converter 801, a subcarrier mapper 803, an M-point inverse discrete Fourier transform (IDFT) module 804, and a parallel-to-serial converter 805. Each input signal that is input to the S/P converter 801 may be a channel coded and modulated data symbol. However, a UE for transmitting signals according to the SC-FDMA scheme may further include an N-point discrete Fourier transform (DFT) module 802. The influence of IDFT processing of the M-point IDFT module 804 is considerably offset, such that a transmission signal may be designed to have a single carrier property. That is, the DFT module 802 performs DFT spreading of an input data symbol such that a single carrier property requisite for UL transmission may be satisfied. The SC-FDMA transmission scheme basically provides good or superior Peak to Average Power ratio (PAPR) or Cubic Metric (CM), such that the UL transmitter can more effectively transmit data or information even in the case of the power limitation situation, resulting in an increase in user throughput.
FIG. 9 illustrates maximum transmission power for single antenna transmission and MIMO transmission. FIG. 9(a) shows the case of single antenna transmission. As can be seen from FIG. 9(a), one power amplifier (PA) may be provided to one antenna. In FIG. 9(a), an output signal (Pmax) of the power amplifier (PA) may have a specific value, for example, 23 dBm. In contrast, FIGS. 9(b) and 9(c) show the case of MIMO transmission. As can be seen from FIGS. 9(b) and 9(c), several PAs may be mapped to respective Tx antennas. For example, provided that the number of Tx antennas is set to 2, 2 PAs may be mapped to respective Tx antennas. The setting of output values (i.e., maximum Tx power) of 2 PAs may be configured in different ways as shown in FIGS. 9(b) and 9(c).
In FIG. 9(b), maximum transmission power (Pmax) for single antenna transmission may be divisionally applied to PA1 and PA2. That is, if a transmission power value of x [dBm] is assigned to PA1, a transmission power value of (Pmax−x) [dBm] may be applied to PA2. In this case, since total transmission power (Pmax) is maintained, the transmitter may have higher robustness against the increasing PAPR in the power limitation situation.
On the other hand, as can be seen from FIG. 9(c), only one Tx antenna (ANT1) may have a maximum transmission power value (Pmax), and the other Tx antenna (ANT2) may have a half value (Pmax/2) of the maximum transmission power value (Pmax). In this case, only one transmission antenna may have higher robustness against increasing PAPR.
MIMO System
MIMO technology is not dependent on one antenna path to receive a message, collects a plurality of data pieces received via several antennas, and completes total data. As a result, MIMO technology can increase a data transfer rate within a specific range, or can increase a system range at a specific data transfer rate. Under this situation, MIMO technology is a next-generation mobile communication technology capable of being widely applied to mobile communication terminals or RNs. MIMO technology can extend the range of data communication, so that it can overcome the limited amount of transmission (Tx) data of mobile communication systems reaching a critical situation.
FIG. 10(a) shows the configuration of a general MIMO communication system. Referring to FIG. 10(a), if the number of transmit (Tx) antennas increases to NT, and at the same time the number of receive (Rx) antennas increases to NR, a theoretical channel transmission capacity of the MIMO communication system increases in proportion to the number of antennas, differently from the above-mentioned case in which only a transmitter or receiver uses several antennas, so that transmission rate and frequency efficiency can be greatly increased. In this case, the transfer rate acquired by the increasing channel transmission capacity can theoretically increase by a predetermined amount that corresponds to multiplication of a maximum transfer rate (Ro) acquired when one antenna is used and a rate of increase (Ri). The rate of increase (Ri) can be represented by the following equation 1.

Ri=min(NT,NR)  [Equation 1]

For example, provided that a MIMO system uses four Tx antennas and four Rx antennas, the MIMO system can theoretically acquire a high transfer rate which is four times higher than that of a single antenna system. After the above-mentioned theoretical capacity increase of the MIMO system was demonstrated in the mid-1990s, many developers began to conduct intensive research into a variety of technologies which can substantially increase data transfer rate using the theoretical capacity increase. Some of the above technologies have been reflected in a variety of wireless communication standards, for example, third-generation mobile communication or next-generation wireless LAN, etc.
A variety of MIMO-associated technologies have been intensively researched by many companies or developers, for example, research into information theory associated with MIMO communication capacity under various channel environments or multiple access environments, research into a radio frequency (RF) channel measurement and modeling of the MIMO system, and research into a space-time signal processing technology.
Mathematical modeling of a communication method for use in the above-mentioned MIMO system will hereinafter be described in detail. As can be seen from FIG. 10(a), it is assumed that there are NT Tx antennas and NR Rx antennas. In the case of a transmission signal, a maximum number of transmission information pieces is NT under the condition that NT Tx antennas are used, so that the transmission information can be represented by a specific vector shown in the following equation 2.

s=└s1,s2, . . . , sNT┘T  [Equation 2]

In the meantime, individual transmission information pieces s1, s2, . . . , sNT may have different transmission powers. In this case, if the individual transmission powers are denoted by P1, P2, . . . , PNT, transmission information having an adjusted transmission power can be represented by a specific vector shown in the following equation 3.

ŝ=[ŝ1,ŝ2, . . . , ŝNT]T=[P1s1,P2s2, . . . , PNTsNT]T  [Equation 3]

In Equation 3, ŝ is a transmission vector, and can be represented by the following equation 4 using a diagonal matrix P of a transmission power.




  
    
      
        
          s
          ^
        
        =
        
          
            
              [
              
                
                  
                    
                      P
                      1
                    
                  
                  
                    
                      
                    
                  
                  
                    
                      
                    
                  
                  
                    0
                  
                
                
                  
                    
                      
                    
                  
                  
                    
                      P
                      2
                    
                  
                  
                    
                      
                    
                  
                  
                    
                      
                    
                  
                
                
                  
                    
                      
                    
                  
                  
                    
                      
                    
                  
                  
                    ⋱
                  
                  
                    
                      
                    
                  
                
                
                  
                    0
                  
                  
                    
                      
                    
                  
                  
                    
                      
                    
                  
                  
                    
                      P
                      
                        N
                        T
                      
                    
                  
                
              
              ]
            
            ⁡
            
              [
              
                
                  
                    
                      s
                      1
                    
                  
                
                
                  
                    
                      s
                      2
                    
                  
                
                
                  
                    ⋮
                  
                
                
                  
                    
                      s
                      
                        N
                        T
                      
                    
                  
                
              
              ]
            
          
          =
          Ps
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          4
        
        ]
      
    
  




In the meantime, the information vector ŝ having an adjusted transmission power is applied to a weight matrix W, so that NT transmission signals x1, x2, . . . , xNT to be actually transmitted are configured. In this case, the weight matrix W is adapted to properly distribute transmission information to individual antennas according to transmission channel situations. The above-mentioned transmission signals x1, x2, . . . , xNT can be represented by the following equation 5 using the vector X. Here, Wi,j denotes a weight corresponding to i-th Tx antenna and j-th information. W represents a weight matrix or precoding matrix.




  
    
      
        x
        =
        
           
          
            
              [
              
                
                  
                    
                      x
                      1
                    
                  
                
                
                  
                    
                      x
                      2
                    
                  
                
                
                  
                    ⋮
                  
                
                
                  
                    
                      x
                      i
                    
                  
                
                
                  
                    ⋮
                  
                
                
                  
                    
                      x
                      
                        N
                        T
                      
                    
                  
                
              
              ]
            
            =
            
              
                
                  [
                  
                    
                      
                        
                          w
                          11
                        
                      
                      
                        
                          w
                          12
                        
                      
                      
                        ...
                      
                      
                        
                          w
                          
                            1
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                    
                      
                        
                          w
                          21
                        
                      
                      
                        
                          w
                          22
                        
                      
                      
                        ...
                      
                      
                        
                          w
                          
                            2
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                    
                      
                        ⋮
                      
                      
                        
                          
                        
                      
                      
                        ⋱
                      
                      
                        
                          
                        
                      
                    
                    
                      
                        
                          w
                          
                            i
                            ⁢
                            
                              
                            
                            ⁢
                            1
                          
                        
                      
                      
                        
                          w
                          
                            i
                            ⁢
                            
                              
                            
                            ⁢
                            2
                          
                        
                      
                      
                        ...
                      
                      
                        
                          w
                          
                            iN
                            T
                          
                        
                      
                    
                    
                      
                        ⋮
                      
                      
                        
                          
                        
                      
                      
                        ⋱
                      
                      
                        
                          
                        
                      
                    
                    
                      
                        
                          w
                          
                            
                              N
                              T
                            
                            ⁢
                            1
                          
                        
                      
                      
                        
                          w
                          
                            
                              N
                              T
                            
                            ⁢
                            2
                          
                        
                      
                      
                        ...
                      
                      
                        
                          w
                          
                            
                              N
                              T
                            
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                  
                  ]
                
                ⁡
                
                  [
                  
                    
                      
                        
                          
                            s
                            ^
                          
                          1
                        
                      
                    
                    
                      
                        
                          
                            s
                            ^
                          
                          2
                        
                      
                    
                    
                      
                        ⋮
                      
                    
                    
                      
                        
                          
                            s
                            ^
                          
                          j
                        
                      
                    
                    
                      
                        ⋮
                      
                    
                    
                      
                        
                          
                            s
                            ^
                          
                          
                            N
                            T
                          
                        
                      
                    
                  
                  ]
                
              
              =
              
                
                  W
                  ⁢
                  
                    s
                    ^
                  
                
                =
                WPs
              
            
          
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          5
        
        ]
      
    
  




When NR Rx antennas are used, received signals y1, y2, . . . , yNR of individual antennas can be represented by a specific vector (y) shown in the following equation 6.

y=[y1,y2, . . . , yNR]T  [Equation 6]

In the meantime, if a channel modeling is executed in the MIMO communication system, individual channels can be distinguished from each other according to Tx/Rx antenna indexes. A specific channel passing the range from a Tx antenna j to a Rx antenna i is denoted by hij. In this case, it should be noted that the index order of the channel hij is located before a Rx antenna index and is located after a Tx antenna index.
Several channels are tied up, so that they are displayed in the form of a vector or matrix. An exemplary vector is as follows. FIG. 10(b) shows channels from NT Tx antennas to a Rx antenna i.
Referring to FIG. 10(b), the channels passing the range from the NT Tx antennas to the Rx antenna i can be represented by the following equation 7.

hiT=└hi1,hi2, . . . , hiNT┘  [Equation 7]

If all channels passing the range from the NT Tx antennas to NR Rx antennas are denoted by the matrix shown in Equation 7, the following equation 8 is acquired.




  
    
      
        H
        =
        
          
            [
            
              
                
                  
                    h
                    1
                    T
                  
                
              
              
                
                  
                    h
                    2
                    T
                  
                
              
              
                
                  ⋮
                
              
              
                
                  
                    h
                    i
                    T
                  
                
              
              
                
                  ⋮
                
              
              
                
                  
                    h
                    
                      N
                      R
                    
                    T
                  
                
              
            
            ]
          
          =
          
            [
            
              
                
                  
                    h
                    11
                  
                
                
                  
                    h
                    12
                  
                
                
                  ...
                
                
                  
                    h
                    
                      1
                      ⁢
                      
                        N
                        T
                      
                    
                  
                
              
              
                
                  
                    h
                    21
                  
                
                
                  
                    h
                    22
                  
                
                
                  ...
                
                
                  
                    h
                    
                      2
                      ⁢
                      
                        N
                        T
                      
                    
                  
                
              
              
                
                  ⋮
                
                
                  
                    
                  
                
                
                  ⋱
                
                
                  
                    
                  
                
              
              
                
                  
                    h
                    
                      i
                      ⁢
                      
                        
                      
                      ⁢
                      1
                    
                  
                
                
                  
                    h
                    
                      i
                      ⁢
                      
                        
                      
                      ⁢
                      2
                    
                  
                
                
                  ...
                
                
                  
                    h
                    
                      iN
                      T
                    
                  
                
              
              
                
                  ⋮
                
                
                  
                    
                  
                
                
                  ⋱
                
                
                  
                    
                  
                
              
              
                
                  
                    h
                    
                      
                        N
                        R
                      
                      ⁢
                      1
                    
                  
                
                
                  
                    h
                    
                      
                        N
                        R
                      
                      ⁢
                      2
                    
                  
                
                
                  ...
                
                
                  
                    h
                    
                      
                        N
                        R
                      
                      ⁢
                      
                        N
                        T
                      
                    
                  
                
              
            
            ]
          
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          8
        
        ]
      
    
  




Additive white Gaussian noise (AWGN) is added to an actual channel which has passed the channel matrix H shown in Equation 8. The AWGN n1, n2, . . . , nNR added to each of NR Rx antennas can be represented by a specific vector shown in the following equation 9.

n=└n1,n2, . . . , nNR┘T  [Equation 9]

A reception signal calculated by the above-mentioned equations can be represented by the following equation 10.




  
    
      
        y
        =
        
          
            [
            
              
                
                  
                    y
                    1
                  
                
              
              
                
                  
                    y
                    2
                  
                
              
              
                
                  ⋮
                
              
              
                
                  
                    y
                    i
                  
                
              
              
                
                  ⋮
                
              
              
                
                  
                    y
                    
                      N
                      R
                    
                  
                
              
            
            ]
          
          =
          
            
              
                
                  [
                  
                    
                      
                        
                          h
                          11
                        
                      
                      
                        
                          h
                          12
                        
                      
                      
                        ...
                      
                      
                        
                          h
                          
                            1
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                    
                      
                        
                          h
                          21
                        
                      
                      
                        
                          h
                          22
                        
                      
                      
                        ...
                      
                      
                        
                          h
                          
                            2
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                    
                      
                        ⋮
                      
                      
                        
                          
                        
                      
                      
                        ⋱
                      
                      
                        
                          
                        
                      
                    
                    
                      
                        
                          h
                          
                            i
                            ⁢
                            
                              
                            
                            ⁢
                            1
                          
                        
                      
                      
                        
                          h
                          
                            i
                            ⁢
                            
                              
                            
                            ⁢
                            2
                          
                        
                      
                      
                        ...
                      
                      
                        
                          h
                          
                            iN
                            T
                          
                        
                      
                    
                    
                      
                        ⋮
                      
                      
                        
                          
                        
                      
                      
                        ⋱
                      
                      
                        
                          
                        
                      
                    
                    
                      
                        
                          h
                          
                            
                              N
                              R
                            
                            ⁢
                            1
                          
                        
                      
                      
                        
                          h
                          
                            
                              N
                              R
                            
                            ⁢
                            2
                          
                        
                      
                      
                        ...
                      
                      
                        
                          h
                          
                            
                              N
                              R
                            
                            ⁢
                            
                              N
                              T
                            
                          
                        
                      
                    
                  
                  ]
                
                ⁡
                
                  [
                  
                    
                      
                        
                          x
                          1
                        
                      
                    
                    
                      
                        
                          x
                          2
                        
                      
                    
                    
                      
                        ⋮
                      
                    
                    
                      
                        
                          x
                          j
                        
                      
                    
                    
                      
                        ⋮
                      
                    
                    
                      
                        
                          x
                          
                            N
                            T
                          
                        
                      
                    
                  
                  ]
                
              
              +
              
                [
                
                  
                    
                      
                        n
                        1
                      
                    
                  
                  
                    
                      
                        n
                        2
                      
                    
                  
                  
                    
                      ⋮
                    
                  
                  
                    
                      
                        n
                        i
                      
                    
                  
                  
                    
                      ⋮
                    
                  
                  
                    
                      
                        n
                        
                          N
                          R
                        
                      
                    
                  
                
                ]
              
            
            =
            
              Hx
              +
              n
            
          
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          10
        
        ]
      
    
  




In the meantime, the number of rows and the number of columns of a channel matrix H indicating a channel condition are determined by the number of Tx/Rx antennas. In the channel matrix H, the number of rows is equal to the number (NR) of Rx antennas, and the number of columns is equal to the number (NT) of Tx antennas. Namely, the channel matrix H is denoted by an NR×NT matrix. Generally, a matrix rank is defined by a smaller number between the number of rows and the number of columns, in which the rows and the columns are independent of each other. Therefore, the matrix rank cannot be higher than the number of rows or columns. The rank of the channel matrix H can be represented by the following equation 11.

rank(H)≦min(NT,NR)  [Equation 11]

A variety of MIMO transmission/reception schemes may be used for operating the MIMO system, for example, frequency switched transmit diversity (FSTD), Space Frequency Block Coding (SFBC), Space Time Block Coding (STBC), Cyclic Delay Diversity (CDD), time switched transmit diversity (TSTD), etc. In case of Rank 2 or higher, Spatial Multiplexing (SM), Generalized Cyclic Delay Diversity (GCDD), Selective Virtual Antenna Permutation (S-VAP), etc. may be used.
The FSTD scheme serves to allocate subcarriers having different frequencies to signals transmitted through multiple antennas so as to obtain diversity gain. The SFBC scheme efficiently applies selectivity of a spatial region and a frequency region so as to obtain diversity gain and multiuser scheduling gain. The STBC scheme applies selectivity of a spatial domain and a time region. The CDD scheme serves to obtain diversity gain using path delay between transmit antennas. The TSTD scheme serves to temporally divide signals transmitted through multiple antennas. The spatial multiplexing scheme serves to transmit different data through different antennas so as to increase a transfer rate. The GCDD scheme serves to apply selectivity of a time region and a frequency region. The S-VAP scheme uses a single precoding matrix and includes a Multi Codeword (MCW) S-VAP for mixing multiple codewords among antennas in spatial diversity or spatial multiplexing and a Single Codeword (SCW) S-VAP using a single codeword.
In case of the STBC scheme from among the above-mentioned MIMO transmission schemes, the same data symbol is repeated to support orthogonality in a time domain so that time diversity can be obtained. Similarly, the SFBC scheme enables the same data symbol to be repeated to support orthogonality in a frequency domain so that frequency diversity can be obtained. An exemplary time block code used for STBC and an exemplary frequency block code used for SFBC are shown in Equation 12 and Equation 13, respectively. Equation 12 shows a block code of the case of 2 Tx antennas, and Equation 13 shows a block code of the case of 4 Tx antennas.




  
    
      
        
          1
          
            2
          
        
        ⁢
        
          (
          
            
              
                
                  S
                  1
                
              
              
                
                  S
                  2
                
              
            
            
              
                
                  -
                  
                    S
                    2
                    *
                  
                
              
              
                
                  S
                  1
                  *
                
              
            
          
          )
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          12
        
        ]
      
    
  
  
    
      
        
          1
          
            2
          
        
        ⁢
        
          (
          
            
              
                
                  S
                  1
                
              
              
                
                  S
                  2
                
              
              
                0
              
              
                0
              
            
            
              
                0
              
              
                0
              
              
                
                  S
                  3
                
              
              
                
                  S
                  4
                
              
            
            
              
                
                  -
                  
                    S
                    2
                    *
                  
                
              
              
                
                  S
                  1
                  *
                
              
              
                0
              
              
                0
              
            
            
              
                0
              
              
                0
              
              
                
                  -
                  
                    S
                    4
                    *
                  
                
              
              
                
                  S
                  3
                  *
                
              
            
          
          )
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          13
        
        ]
      
    
  




In Equations 12 and 13, Si (i=1, 2, 3, 4) means a modulated data symbol. In addition, each row of the matrixes of Equation 12 and 13 may indicate an antenna port, and each column may indicate time (in case of STBC) or frequency (in case of SFBC).
On the other hand, the CDD scheme from among the above-mentioned MIMO transmission schemes mandatorily increases delay spread so as to increase frequency diversity. FIG. 11 is a conceptual diagram illustrating a general CDD structure for use in the MIMO system. FIG. 11(a) shows a method for applying cyclic delay to a time domain. If necessary, the CDD scheme based on the cyclic delay of FIG. 11(a) may also be implemented as phase-shift diversity of FIG. 11(b).
In association with the above-mentioned MIMO transmission techniques, the codebook-based precoding method will hereinafter be described with reference to FIG. 12. FIG. 12 is a conceptual diagram illustrating codebook-based precoding.
In accordance with the codebook-based precoding scheme, a transceiver may share codebook information including a predetermined number of precoding matrixes according to a transmission rank, the number of antennas, etc. That is, if feedback information is finite, the precoding-based codebook scheme may be used. The receiver measures a channel state through a reception signal, so that a finite number of preferred precoding matrix information (i.e., an index of the corresponding precoding matrix) may be fed back to the transmitter on the basis of the above-mentioned codebook information. For example, the receiver may select an optimum precoding matrix by measuring an ML (Maximum Likelihood) or MMSE (Minimum Mean Square Error) scheme. Although the receiver shown in FIG. 12 transmits precoding matrix information for each codeword to the transmitter, the scope or spirit of the present invention is not limited thereto.
Upon receiving feedback information from the receiver, the transmitter may select a specific precoding matrix from a codebook on the basis of the received information. The transmitter that has selected the precoding matrix performs a precoding operation by multiplying the selected precoding matrix by as many layer signals as the number of transmission ranks, and may transmit each precoded Tx signal over a plurality of antennas.
Upon reception of the precoded signal from the transmitter as an input, the receiver performs inverse processing of the precoding having been conducted in the transmitter to recover the reception (Rx) signal. Generally, the precoding matrix satisfies a unitary matrix U such as U*UH=I, so that the inverse processing of the above-mentioned precoding may be conducted by multiplying a Hermit matrix PH of the precoding matrix H used in the precoding of the transmitter by the reception (Rx) signal.
Physical Uplink Control Channel (PUCCH)
PUCCH including UL control information will hereinafter be described in detail.
A plurality of UE control information pieces may be transmitted through a PUCCH. When code division multiplexing (CDM) is performed in order to discriminate signals of UEs, a constant amplitude zero autocorrelation (CAZAC) sequence having a length of 12 is mainly used. Since the CAZAC sequence has a property that a constant amplitude is maintained in the time domain and frequency domain, a peak-to-average power ratio (PAPR) of a UE or cubic metric (CM) may be decreased to increase coverage. In addition, ACK/NACK information for DL data transmitted through the PUCCH may be covered using an orthogonal sequence.
In addition, control information transmitted through the PUCCH may be discriminated using cyclically shifted sequences having different cyclic shift values. A cyclically shifted sequence may be generated by cyclically shifting a basic sequence (also called a base sequence) by a specific cyclic shift (CS) amount. The specific CS amount is indicated by a CS index. The number of available CSs may be changed according to channel delay spread. Various sequences may be used as the basic sequence and examples thereof include the above-described CAZAC sequence.
PUCCH may include a variety of control information, for example, a scheduling request (SR), DL channel measurement information, and ACK/NACK information for DL data transmission. The channel measurement information may include a channel quality indicator (CQI), a precoding matrix index (PMI), and a rank indicator (RI).
PUCCH format may be defined according to the type of control information contained in a PUCCH, modulation scheme information thereof, etc. That is, PUCCH format 1 may be used for SR transmission, PUCCH format 1a or 1b may be used for HARQ ACK/NACK transmission, PUCCH format 2 may be used for CQI transmission, and PUCCH format 2a/2b may be used for HARQ ACK/NACK transmission.
If HARQ ACK/NACK is transmitted alone in an arbitrary subframe, PUCCH format 1a or 1b may be used. If SR is transmitted alone, PUCCH format 1 may be used. The UE may transmit the HARQ ACK/NACK and the SR through the same subframe, and a detailed description thereof will hereinafter be described in detail.
PUCCH format may be summarized as shown in Table 1.











TABLE 1







Number of




PUCCH
Modulation 
bits per




format
scheme
subframe
Usage
etc.







1
N/A
N/A
SR(Scheduling 






Request)



1a
BPSK
 1
ACK/NACK
One codeword


1b
QPSK
 2
ACK/NACK
Two codeword


2
QPSK
20
CQI
Joint Coding






ACK/NACK






(extended CP)


2a
QPSK + 
21
CQI + ACK/
Normal CP only



BPSK

NACK



2b
QPSK + 
22
CQI + ACK/
Normal CP only



BPSK

NACK









FIG. 13 shows a PUCCH resource mapping structure for use in a UL physical resource block (PRB). NRBUL is the number of RBs for use in uplink (UL), and nPRB is a PRB number. PUCCH may be mapped to both edges of a UL frequency block. CQI resources may be mapped to a PRB located just after the edge of a frequency band, and ACK/NACK may be mapped to this PRB.
PUCCH format 1 is a control channel used for SR transmission. SR may be transmitted in such a manner that SR is requested or not requested.
PUCCH format 1a/1b is a control channel used for ACK/NACK transmission. In the PUCCH format 1a/1b, a symbol modulated using the BPSK or QPSK modulation scheme is multiplied by a CAZAC sequence of length 12. Upon completion of the CAZAC sequence multiplication, the resultant symbol is blockwise-spread as an orthogonal sequence. A Hadamard sequence of length 4 is applied to general ACK/NACK information, and a DFT (Discrete Fourier Transform) sequence of length 3 is applied to shortened ACK/NACK information and a reference signal (or reference symbol; RS). A Hadamard sequence of length 2 may be applied to the reference signal for the extended CP.
The UE may also transmit HARQ ACK/NACK and SR through the same subframe. For positive SR transmission, the UE may transmit HARQ ACK/NACK information through resources allocated for the SR. For negative SR transmission, the UE may transmit HARQ ACK/NACK information through resources allocated for ACK/NACK information.
PUCCH format 2/2a/2b will hereinafter be described in detail. PUCCH format 2/2a/2b is a control channel for transmitting channel measurement feedback (CQI, PMI, RI).
The PUCCH format 2/2a/2b may support modulation based on a CAZAC sequence, and a QPSK-modulated symbol may be multiplied by a CAZAC sequence of length 12. Cyclic shift (CS) of the sequence may be changed between a symbol and a slot. For a reference signal (RS), orthogonal covering may be used.
FIG. 14 shows a channel structure of a CQI bit. The CQI bit may include one or more fields. For example, the CQI bit may include a CQI field indicating a CQI index for MCS decision, a PMI field indicating an index of a precoding matrix of a codebook, and an RI field indicating rank.
Referring to FIG. 14(a), a reference signal (RS) may be loaded on two SC-FDMA symbols spaced apart from each other by a predetermined distance corresponding to 3 SC-FDMA symbol intervals from among 7 SC-FDMA symbols contained in one slot, and CQI may be loaded on the remaining 5 SC-FDMA symbols. The reason why two RSs may be used in one slot is to support a high-speed UE. In addition, each UE may be discriminated by a sequence. CQI symbols may be modulated in the entire SC-FDMA symbol, and the modulated CQI symbols may then be transmitted. The SC-FDMA symbol is composed of one sequence. That is, a UE performs CQI modulation using each sequence, and transmits the modulated result.
The number of symbols that can be transmitted during one TTI is set to 10, and CQI modulation is extended up to QPSK. If QPSK mapping is applied to the SC-FDMA symbol, a CQI value of 2 bits may be loaded on the SC-FDMA symbol, so that a CQI value of 10 bits may be assigned to one slot. Therefore, a maximum of 20-bit CQI value may be assigned to one subframe. A frequency domain spreading code may be used to spread CQI in the frequency domain.
CAZAC sequence (for example, a ZC sequence) may be used as a frequency domain spread code. In addition, another sequence having superior correlation characteristics may be used as the frequency domain spread code. Specifically, CAZAC sequences having different cyclic shift (CS) values may be applied to respective control channels, such that the CAZAC sequences may be distinguished from one another. IFFT may be applied to the frequency domain spread CQI.
FIG. 14(b) shows the example of PUCCH format 2/2a/2b transmission in case of the extended CP. One slot includes 6 SC-FDMA symbols. RS is assigned to one OFDM symbol from among 6 OFDM symbols of each slot, and a CQI bit may be assigned to the remaining 5 OFDM symbols. Except for the six SC-FDMA symbols, the example of the normal CP of FIG. 14(a) may be used without change.
Orthogonal covering applied to the RS of FIGS. 14(a) and 14(b) is shown in Table 2.










TABLE 2







Normal CP
Extended CP









[1 1]
[1]










Simultaneous transmission of CQI and ACK/NACK information will hereinafter be described with reference to FIG. 15.
In case of the normal CP, CQI and ACK/NACK information can be simultaneously transmitted using PUCCH format 2a/2b. ACK/NACK information may be transmitted through a symbol where CQI RS is transmitted. That is, a second RS for use in the normal CP may be modulated into an ACK/NACK symbol. In the case where the ACK/NACK symbol is modulated using the BPSK scheme as shown in the PUCCH format 1a, CQI RS may be modulated into the ACK/NACK symbol according to the BPSK scheme. In the case where the ACK/NACK symbol is modulated using the QPSK scheme as shown in the PUCCH format 1b, CQI RS may be modulated into the ACK/NACK symbol according to the QPSK scheme. On the other hand, in case of the extended CP, CQI and ACK/NACK information are simultaneously transmitted using the PUCCH format 2. For this purpose, CQI and ACK/NACK information may be joint-coded.
For details of PUCCH other than the above-mentioned description, the 3GPP standard document (e.g., 3GPP TS36.211 5.4) may be referred to, and detailed description thereof will herein be omitted for convenience of description. However, it should be noted that PUCCH contents disclosed in the above-mentioned standard document can also be applied to a PUCCH used in various embodiments of the present invention without departing from the scope or spirit of the present invention.
Channel State Information (CSI) Feedback
In order to correctly perform MIMO technology, the receiver may feed back a rank indicator (RI), a precoding matrix index (PMI) and channel quality indicator (CQI) to the transmitter. RI, PMI and CQI may be generically named Channel state Information (CSI) as necessary. Alternatively, the term “CQI” may be used as the concept of channel information including RI, PMI and CQI.
FIG. 16 is a conceptual diagram illustrating a feedback of channel state information.
Referring to FIG. 16, MIMO transmission data from a transmitter may be received at a receiver over a channel II. The receiver may select a preferred precoding matrix from a codebook on the basis of the received signal, and may feed back the selected PMI to the transmitter. In addition, the receiver may measure a Signal-to-Interference plus Noise Ratio (SINR) of the reception (Rx) signal, calculate channel quality information (CQI), and feed back the calculated CQI to the transmitter. In addition, the receiver may feed back a rank indicator (RI) of the Rx signal to the transmitter. The transmitter may determine the number of layers suitable for data transmission to the receiver and time/frequency resources, MCS (Modulation and Coding Scheme), etc. using RI and CQI fed back from the receiver. In addition, the transmitter may transmit the precoded Tx signal using the precoding matrix (Wl) indicated by a PMI fed back from the receiver over a plurality of antennas.
Channel state information will hereinafter be described in detail.
RI is information regarding a channel rank (i.e., the number of layers for data transmission of a transmitter). RI may be determined by the number of allocated Tx layers, and may be acquired from associated downlink control information (DCI).
PMI is information regarding a precoding matrix used for data transmission of a transmitter. The precoding matrix fed back from the receiver may be determined considering the number of layers indicated by RI. PMI may be fed back in case of closed-loop spatial multiplexing (SM) and large delay cyclic delay diversity (CDD). In the case of open-loop transmission, the transmitter may select a precoding matrix according to predetermined rules. A process for selecting a PMI for each rank (rank 1 to 4) is as follows. The receiver may calculate a post processing SINR in each PMI, convert the calculated SINR into the sum capacity, and select the best PMI on the basis of the sum capacity. That is, PMI calculation of the receiver may be considered to be a process for searching for an optimum PMI on the basis of the sum capacity. The transmitter that has received PMI feedback from the receiver may use a precoding matrix recommended by the receiver. This fact may be contained as a 1-bit indicator in scheduling allocation information for data transmission to the receiver. Alternatively, the transmitter may not use the precoding matrix indicated by a PMI fed back from the transmitter. In this case, precoding matrix information used for data transmission from the transmitter to the receiver may be explicitly contained in the scheduling allocation information. For details of PMI, the 3GPP standard document (e.g., 3GPP TS36.211) may be referred to.
CQI is information regarding channel quality. CQI may be represented by a predetermined MCS combination. CQI index may be given as shown in the following table 3.












TABLE 3







CQI index
modulation
code rate × 1024
efficiency



















0
out of range












1
QPSK
 78
0.1523



2
QPSK
120
0.2344



3
QPSK
193
0.3770



4
QPSK
308
0.6016



5
QPSK
449
0.8770



6
QPSK
602
1.1758



7
16QAM
378
1.4766



8
16QAM
490
1.9141



9
16QAM
616
2.4063



10
64QAM
466
2.7305



11
64QAM
567
3.3223



12
64QAM
666
3.9023



13
64QAM
772
4.5234



14
64QAM
873
5.1152



15
64QAM
948
5.5547










Referring to Table 3, CQI index may be represented by 4 bits (i.e., CQI indexes of 0 ̃15). Each CQI index may indicate a modulation scheme and a code rate.
A CQI calculation method will hereinafter be described. The following assumptions (1) to (5) for allowing a UE to calculate a CQI index are defined in the 3GPP standard document (e.g., 3GPP TS36.213).
(1) The first three OFDM symbols in one subframe are occupied by control signaling.
(2) Resource elements (REs) used by a primary synchronization signal, a secondary synchronization signal or a physical broadcast channel (PBCH) are not present.
(3) CP length of a non-MBSFN subframe is assumed.
(4) Redundancy version is set to zero (0).
(5) PDSCH transmission method may be dependent upon a current transmission mode (e.g., a default mode) configured in a UE.
(6) The ratio of PDSCH EPRE (Energy Per Resource Element) to a cell-specific reference signal EPRE may be given with the exception of ρA. (A detailed description of ρA may follow the following assumption. Provided that a UE for an arbitrary modulation scheme may be set to a Transmission Mode 2 having four cell-specific antenna ports or may be set to a Transmission Mode 3 having an RI of 1 and four cell-specific antenna ports, ρA may be denoted by ρA=PA+Δoffset10 log10(2)[dB]. In the remaining cases, in association with an arbitrary modulation method and the number of arbitrary layers, ρA may be denoted by ρA=PA+Δoffset[dB]. Δoffset is given by a nomPDSCH-RS-EPRE-Offset parameter configured by higher layer signaling).
Definition of the above-mentioned assumptions may indicate that CQI includes not only information regarding channel quality but also various information of a corresponding UE. That is, different CQI indexes may be fed back according to a throughput or performance of the corresponding UE at the same channel quality, so that it is necessary to define a predetermined reference for the above-mentioned assumption.
The UE may receive a downlink reference signal (DL RS) from an eNB, and recognize a channel state on the basis of the received DL RS. In this case, the RS may be a common reference signal (CRS) defined in the legacy 3GPP LTE system, and may be a Channel state Information Reference Signal (CSI-RS) defined in a system (e.g., 3GPP LTE-A system) having an extended antenna structure. The UE may satisfy the assumption given for CQI calculation at a channel recognized through a reference signal (RS), and at the same time calculate a CQI index in which a Block Error Rate (BLER) is not higher than 10%. The UE may transmit the calculated CQI index to the eNB. The UE may not apply a method for improving interference estimation to a CQI index calculation process.
The process for allowing the UE to recognize a channel state and determine an appropriate MCS may be defined in various ways in terms of UE implementation. For example, the UE may calculate a channel state or an effective SINR using a reference signal (RS). In addition, the channel state or the effective SINR may be measured on the entire system bandwidth (also called ‘Set S’) or may also be measured on some bandwidths (specific subband or specific RB). The CQI for the set S may be referred to as a Wideband (WB) CQI, and the CQI for some bandwidths may be referred to as a subband (SB) CQI. The UE may determine the best MCS on the basis of the calculated channel state or effective SINR. The best MCS may indicate an MCS that satisfies the CQI calculation assumption without exceeding a transport block error rate of 10% during the decoding. The UE may determine a CQI index related to the MCS and may report the determined CQI index to the eNB.
Further, CQI-only transmission may be considered in which a UE transmits CQI aperiodically without having data on a PUSCH. Aperiodic CQI transmission may be event-triggered upon receiving a request from the eNB. Such request from the eNB may be a CQI request defined by one bit of DCI format 0. In addition, for CQI-only transmission, MCS index IMCS of 29 may be signaled as shown in the following table 4. In this case, the CQI request bit of the DCI format 0 is set to 1, transmission of 4 RBs or less may be configured, Redundancy Version 1 (RV1) is indicated in PUSCH data retransmission, and a modulation order (Qm) may be set to 2. In other words, in the case of CQI-only transmission, only a QPSK (Quadrature Phase Shift Keying) scheme may be used as a modulation scheme.












TABLE 4







MCS
Modulation
TBS
Redundancy



Index
Order
Index
Version



IMCS
Q′m
ITBS
rvidx





















0
2
0
0



1
2
1
0



2
2
2
0



3
2
3
0



4
2
4
0



5
2
5
0



6
2
6
0



7
2
7
0



8
2
8
0



9
2
9
0



10
2
10
0



11
4
10
0



12
4
11
0



13
4
12
0



14
4
13
0



15
4
14
0



16
4
15
0



17
4
16
0



18
4
17
0



19
4
18
0



20
4
19
0



21
6
19
0



22
6
20
0



23
6
21
0



24
6
22
0



25
6
23
0



26
6
24
0



27
6
25
0



28
6
26
0











29
reserved
1



30

2



31

3










The CQI reporting operation will hereinafter be described in detail.
In 3GPP LTE, when a DL reception entity (e.g., UE) is coupled to a DL transmission entity (e.g., eNB), a reference signal received power (RSRP) and a reference signal received quality (RSRQ) that are transmitted via downlink are measured at an arbitrary time, and the measured result may be periodically or event-triggeredly reported to the eNB.
In a cellular OFDM wireless packet communication system, each UE may report DL channel information based on a DL channel condition via uplink, and the eNB may determine time/frequency resources and MCS (Modulation and Coding Scheme) so as to transmit data to each UE using DL channel information received from each UE.
In case of the legacy 3GPP LTE system (e.g., 3GPP LTE Release-8 system), such channel information may be composed of Channel Quality Indication (CQI), Precoding Matrix Indicator (PMI), and Rank Indication (RI). All or some of CQI, PMI and RI may be transmitted according to a transmission mode of each UE. CQI may be determined by the received signal quality of the UE. Generally, CQI may be determined on the basis of DL RS measurement. In this case, a CQI value actually applied to the eNB may correspond to an MCS in which the UE maintains a Block Error Rate (BLER) of 10% or less at the measured Rx signal quality and at the same time has a maximum throughput or performance.
In addition, such channel information reporting scheme may be divided into periodic reporting and aperiodic reporting upon receiving a request from the eNB.
Information regarding the aperiodic reporting may be assigned to each UE by a CQI request field of 1 bit contained in uplink scheduling information sent from the eNB to the UE. Upon receiving the aperiodic reporting information, each UE may transmit channel information considering the UE's transmission mode to the eNB over a physical uplink shared channel (PUSCH). If necessary, RI and CQI/PMI need not be transmitted over the same PUSCH.
In case of the aperiodic reporting, a cycle in which channel information is transmitted via a higher layer signal, an offset of the corresponding period, etc. may be signaled to each UE in units of a subframe, and channel information considering a transmission (Tx) mode of each UE may be transmitted to the eNB over a physical uplink control channel (PUCCH) at intervals of a predetermined time. In the case where UL transmission data is present in a subframe in which channel information is transmitted at intervals of a predetermined time, the corresponding channel information may be transmitted together with data over not a PUCCH but a PUSCH together. In case of the periodic reporting over a PUCCH, a limited number of bits may be used as compared to PUSCH. RI and CQI/PMI may be transmitted over the same PUSCH.
If the periodic reporting collides with the aperiodic reporting in the same subframe, only the aperiodic reporting may be performed.
In order to calculate a WB CQI/PMI, the latest transmission RI may be used. In a PUCCH reporting mode, RI may be independent of another RI for use in a PUSCH reporting mode. RI is valid only for CQI/PMI for use in the corresponding PUSCH reporting mode.
The CQI/PMI/RI feedback type for the PUCCH reporting mode may be classified into four feedback types (Type 1 to Type 4). Type 1 is CQI feedback for a user-selected subband. Type 2 is WB CQI feedback and WB PMI feedback. Type 3 is RI feedback. Type 4 is WB CQI feedback.
Referring to Table 5, in the case of periodic reporting of channel information, a reporting mode is classified into four reporting modes (Modes 1-0, 1-1, 2-0 and 2-1) according to CQI and PMI feedback types.









TABLE 5









PMI Feedback Type












No PMI (OL, TD, single-antenna)
Single PMI (CL)





CQI
Wideband
Mode 1-0
Mode 1-1


Feedback

RI (only for Open-Loop SM)
RI


Type

One Wideband CQI (4 bit)
Wideband CQI (4 bit)




when RI > 1, CQI of first codeword
Wideband spatial CQI (3 bit) for RI > 1





Wideband PMI (4 bit)



UE
Mode 2-0
Mode 2-1



Selected
RI (only for Open-Loop SM)
RI




Wideband CQI (4 bit)
Wideband CQI (4 bit)




Best-1 CQI (4 bit) in each BP
Wideband spatial CQI (3 bit) for RI > 1




Best-1 indicator(L-bit label)
Wideband PMI (4 bit)




when RI > 1, CQI of first codeword
Best-1 CQI (4 bit) 1 in each BP





Best-1 spatial CQI (3 bit) for RI > 1





Best-1 indicator (L-bit label)









The reporting mode is classified into a wideband (WB) CQI and a subband (SB) CQI according to a CQI feedback type. The reporting mode is classified into a No-PMI and a Single PMI according to transmission or non-transmission of PMI. As can be seen from Table 5, ‘NO PMI’ may correspond to an exemplary case in which an Open Loop (OL), a Transmit Diversity (TD), and a single antenna are used, and ‘Single PMI” may correspond to an exemplary case in which a closed loop (CL) is used.
Mode 1-0 may indicate an exemplary case in which PMI is not transmitted but only WB CQI is transmitted. In case of Mode 1-0, RI may be transmitted only in the case of OL Spatial Multiplexing (SM), and one WB CQI denoted by 4 bits may be transmitted. If RI is higher than ‘1’, CQI for a first codeword may be transmitted. In case of Mode 1-0, Feedback Type 3 and Feedback Type 4 may be multiplexed at different time points within the predetermined reporting period, and then transmitted. The above-mentioned Mode 1-0 transmission scheme may be referred to as Time Division Multiplexing (TDM)-based channel information transmission.
Mode 1-1 may indicate an exemplary case in which a single PMI and a WB CQI are transmitted. In this case, 4-bit WB CQI and 4-bit WB PMI may be transmitted simultaneously with RI transmission. In addition, if RI is higher than ‘1’, 3-bit WB Spatial Differential CQI may be transmitted. In case of transmission of two codewords, the WB spatial differential CQI may indicate a differential value between a WB CQI index for Codeword 1 and a WB CQI index for Codeword 2. These differential values may be assigned to the set {−4, −3, −2, −1, 0, 1, 2, 3}, and each differential value may be assigned to any one of values contained in the set and be represented by 3 bits. In case of Mode 1-1, Feedback Type 2 and Feedback Type 3 may be multiplexed at different time points within the predetermined reporting period, and then transmitted.
Mode 2-0 may indicate that no PMI is transmitted and CQI of a UE-selected band is transmitted. In this case, RI may be transmitted only in case of open loop spatial multiplexing (OL SM), a WB CQI denoted by 4 bits may be transmitted. In each Bandwidth Part (BP), Best-1 CQI may be transmitted, and Best-1 CQI may be denoted by 4 bits. In addition, an indicator of L bits indicating Best-1 may be further transmitted. If RI is higher than ‘1’, CQI for a first codeword may be transmitted. In case of Mode 2-0, the above-mentioned feedback type 1, feedback type 3, and feedback type 4 may be multiplexed at different time points within a predetermined reporting period, and then transmitted.
Mode 2-1 may indicate an exemplary case in which a single PMI and CQI of a UE-selected band are transmitted. In this case, WB CQI of 4 bits, WB spatial differential CQI of 3 bits, and WB PMI of 4 bits are transmitted simultaneously with RI transmission. In addition, Best-1 CQI of 4 bits and a Best-1 indicator of L bits may be simultaneously transmitted at each bandwidth part (BP). If RI is higher than ‘1’, Best-1 spatial differential CQI of 3 bits may be transmitted. During transmission of two codewords, a differential value between a Best-1 CQI index of Codeword 1 and a Best-1 CQI index of Codeword 2 may be indicated. In Mode 2-1, the above-mentioned feedback type 1, feedback 2, and feedback type 3 may be multiplexed at different time points within a predetermined reporting period, and then transmitted.
In the UE selected SB CQI reporting mode, the size of BP (Bandwidth Part) subband may be defined by the following table 6.









TABLE 6





System Bandwidth
Subband Size k
Bandwidth Parts


NRBDL
(RBs)
(J)







6-7
NA
NA


 8-10
4
1


11-26
4
2


27-63
6
3


 64-110
8
4









Table 6 shows a bandwidth part (BP) configuration and the subband size of each BP according to the size of a system bandwidth. A UE may select a preferred subband within each BP, and calculate CQI for the corresponding subband. In Table 6, if the system bandwidth is set to 6 or 7, this means no application of both the subband size and the number of bandwidth parts (BPs). That is, the system bandwidth of 6 or 7 means application of only WB CQI, no subband state, and a BP of 1.
FIG. 17 shows an example of a UE selected CQI reporting mode. NRBDL is the number of RBs of the entire bandwidth. The entire bandwidth may be divided into N CQI subbands (1, 2, 3, . . . , N). One CQI subband may include k RBs defined in Table 6. If the number of RBs of the entire bandwidth is not denoted by an integer multiple of k, the number of RBs contained in the last CQI subband (i.e., the N-th CQI subband) may be determined by the following equation 14.

NRBDL−k·└NRBDL/k┘  [Equation 14]

In Equation 14, └ ┘ represents a floor operation, and └x┘ or floor(x) represents a maximum integer not higher than ‘x’.
In addition, NJ CQI subbands construct one BP, and the entire bandwidth may be divided into J BPs. UE may calculate a CQI index for one preferred Best-1 CQI subband contained in one BP, and transmit the calculated CQI index over a PUCCH. In this case, a Best-1 indicator indicating which Best-1 CQI subband is selected from one BP may also be transmitted. The Best-1 indicator may be composed of L bits, and L may be represented by the following equation 15.

L=┌ log2NJ┐  [Equation 15]

In Equation 15, ┌ ┐ represents a ceiling operation, and ┌X┐ or ceiling(x) represents a minimum integer not higher than ‘x’.
In the above-mentioned UE selected CQI reporting mode, a frequency band for CQI index calculation may be determined. Hereinafter, a CQI transmission cycle will hereinafter be described in detail.
Each UE may receive information composed of a combination of a transmission cycle of channel information and an offset from an upper layer through RRC signaling. The UE may transmit channel information to an eNB on the basis of the received channel information transmission cycle information.
FIG. 18 is a conceptual diagram illustrating a method for enabling a UE to periodically transmit channel information. For example, if a UE receives combination information in which a channel information transmission cycle is set to 5 and an offset is set to 1, the UE transmits channel information in units of 5 subframes, one subframe offset is assigned in the increasing direction of a subframe index on the basis of the 0th subframe, and channel information may be transmitted over a PUCCH. In this case, the subframe index may be comprised of a combination of a system frame number nf and 20 slot indexes ns (0 ̃19) present in the system frame. One subframe may be comprised of 2 slots, such that the subframe index may be represented by 10×nf+floor(ns/2).
One type for transmitting only WB CQI and the other type for transmitting both WB CQI and SB CQI may be classified according to CQI feedback types. In case of the first type for transmitting only the WB CQI, WB CQI information for the entire band is transmitted at a subframe corresponding to each CQI transmission cycle. The WB periodic CQI feedback transmission cycle may be set to any of 2, 5, 10, 16, 20, 32, 40, 64, 80, or 160 ms or no transmission of the WB periodic CQI feedback transmission cycle may be established. In this case, if it is necessary to transmit PMI according to the PMI feedback type of Table 5, PMI information is transmitted together with CQI. In case of the second type for transmitting both WB CQI and SB CQI, WB CQI and SB CQI may be alternately transmitted.
FIG. 19 is a conceptual diagram illustrating a method for transmitting both WB CQI and SB CQI according to an embodiment of the present invention. FIG. 19 shows an exemplary system comprised of 16 RBs. If a system frequency band is comprised of 16 RBs, for example, it is assumed that two bandwidth parts (BPs) (BP0 and BP1) may be configured, each BP may be composed of 2 subbands (SBs) (SB0 and SB1), and each SB may be composed of 4 RBs. In this case, as previously stated in Table 6, the number of BPs and the size of each SB are determined according to the number of RBs contained in the entire system band, and the number of SBs contained in each BP may be determined according to the number of RBs, the number of BPs and the size of SB.
In case of the type for transmitting both WB CQI and SB CQI, the WB CQI is transmitted in the CQI transmission subframe. In the next transmission subframe, CQI of one SB (i.e., Best-1) having a good channel state from among SB0 and SB1 at BP0 and an index (i.e., Best-1 indicator) of the corresponding SB are transmitted. In the further next transmission subframe, CQI of one SB (i.e., Best-1) having a good channel state from among SB0 and SB1 at BP1 and an index (i.e., Best-1 indicator) of the corresponding SB are transmitted. After transmitting the WB CQI, CQI of individual BPs are sequentially transmitted. In this case, CQI of a BP located between a first WB CQI transmitted once and a second WB CQI to be transmitted after the first WB CQI may be sequentially transmitted one to four times. For example, if the CQI of each BP is transmitted once during a time interval between two WB CQIs, CQIs may be transmitted in the order of WB CQI→BP0 CQI→BP1 CQI→WB CQI. In another example, if the CQI of each BP is transmitted four times during a time interval between two WB CQIs, CQIs may be transmitted in the order of WB CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→WB CQI. Information about the number of sequential transmission times of BP CQI during a time interval between two WB CQIs is signaled through a higher layer. Irrespective of WB CQI or SB CQI, the above-mentioned information about the number of sequential transmission times of BP CQI may be transmitted through a PUCCH in a subframe corresponding to information of a combination of channel information transmission cycle signaled from the higher layer and an offset of FIG. 18.
In this case, if PMI also needs to be transmitted according to the PMI feedback type, PMI information and CQI must be simultaneously transmitted. If PUSCH for UL data transmission is present in the corresponding subframe, CQI and PMI can be transmitted along with data through PUSCH instead of PUCCH.
FIG. 20 is a conceptual diagram illustrating an exemplary CQI transmission scheme when both WB CQI and SB CQI are transmitted. In more detail, provided that combination information in which a channel information transmission cycle is set to 5 and an offset is set to 1 is signaled as shown in FIG. 18, and BP information between two WB CQI/PMI parts is sequentially transmitted once, FIG. 20 shows the example of channel information transmission operation of a UE.
On the other hand, in case of RI transmission, RI may be signaled by information of a combination of one signal indicating how many WB CQI/PMI transmission cycles are used for RI transmission and an offset of the corresponding transmission cycle. In this case, the offset may be defined as a relative offset for a CQI/PMI transmission offset. For example, provided that an offset of the CQI/PMI transmission cycle is set to 1 and an offset of the RI transmission cycle is set to zero, the offset of the RI transmission cycle may be identical to that of the CQI/PMI transmission cycle. The offset of the RI transmission cycle may be defined as a negative value or zero.
FIG. 21 is a conceptual diagram illustrating transmission of WB CQI, SB CQI and RI. In more detail, FIG. 21 shows that, under CQI/PMI transmission of FIG. 20, an RI transmission cycle is one time the WB CQI/PMI transmission cycle and the offset of RI transmission cycle is set to ‘−1’. Since the RI transmission cycle is one time the WB CQI/PMI transmission cycle, the RI transmission cycle has the same time cycle. A relative difference between the RI offset value ‘−1’ and the CQI offset ‘1’ of FIG. 20 is set to ‘−1’, such that RI can be transmitted on the basis of the subframe index ‘0’.
In addition, provided that RI transmission overlaps with WB CQI/PMI transmission or SB CQI/PMI transmission, WB CQI/PMI or SB CQI/PMI may drop. For example, provided that the RI offset is set to ‘0’ instead of ‘−1’, the WB CQI/PMI transmission subframe overlaps with the RI transmission subframe. In this case, WB CQI/PMI may drop and RI may be transmitted.
By the above-mentioned combination, CQI, PMI, and RI may be transmitted, and such information may be transmitted from each UE by RRC signaling of a higher layer. The eNB may transmit appropriate information to each UE in consideration of a channel situation of each UE and a distribution situation of UEs included in the eNB.
Meanwhile, payload sizes of SB CQI, WB CQI/PMI, RI and WB CQI in association with the PUCCH report type may be represented by the following table 7.










TABLE 7







PUCCH


PUCCH Reporting Modes













Report


Mode 1-1
Mode 2-1
Mode 1-0
Mode 2-0


Type
Reported
Mode State
(bits/BP)
(bits/BP)
(bits/BP)
(bits/BP)





1
Sub-band
RI = 1
NA
4 + L
NA
4 + L



CQI
RI > 1
NA
7 + L
NA
4 + L


2
Wideband
2 TX Antennas RI = 1
6
6
NA
NA



CQI/PMI
4 TX Antennas RI = 1
8
8
NA
NA




2 TX Antennas RI > 1
8
8
NA
NA




4 TX Antennas RI > 1
11
11
NA
NA


3
RI
2-layer spatial multiplexing
1
1
1
1




4-layer spatial multiplexing
2
2
2
2


4
Wideband
RI = 1 or RI > 1
NA
NA
4
4



CQI









Aperiodic transmission of CQI, PMI and RI over a PUSCH will hereinafter be described.
In case of the aperiodic reporting, RI and CQI/PMI may be transmitted over the same PUSCH. In case of the aperiodic reporting mode, RI reporting is valid only for CQI/PMI reporting in the corresponding aperiodic reporting mode. CQI-PMI combinations capable of being supported to all the rank values are shown in the following table 8.









TABLE 8









PMI Feedback Type












No PMI (OL, TD, single-antenna)
with PMI (CL)





PUSCH CQI 
Wideband

Mode 1-2: Multiple PMI


Feedback Type
(Wideband CQI)

RI





1st Wideband CQI (4 bit)





2nd Wideband CQI (4 bit) if RI > 1





subband PMIs on each subband



UE Selected 
Mode 2-0
Mode 2-2: Multiple PMI



(Subband CQI)
RI (only for Open-Loop SM)
RI




Wideband CQI (4 bit) + Best-M CQI (2 bit)
lst Wideband CQI (4 bit) + Best-M CQI(2 bit)




Best-M index
2nd Wideband CQI (4 bit) + Best-M CQI(2 bit)




when RI > 1, CQI of first codeword
if RI > 1





Wideband PMI + Best-M PMI





Best-M index



Higher layer-
Mode 3-0
Mode 3-1: Single PMI



configured
RI (only for Open-Loop SM)
RI



(subband CQI)
Wideband CQI (4 bit) + subband CQI (2 bit)
1st Wideband CQI (4 bit) + subband CQI (2 bit)




when RI > 1, CQI of first codeword
2nd Wideband CQI (4bit) + subband CQI (2 bit)





if RI > 1





Wideband PMI









Mode 1-2 of Table 8 indicates a WB feedback. In Mode 1-2, a preferred precoding matrix for each subband may be selected from a codebook subset on the assumption of transmission only in the corresponding subband. The UE may report one WB CQI at every codeword, and WB CQI may be calculated on the assumption that data is transmitted on subbands of the entire system bandwidth (Set S) and the corresponding selected precoding matrix is used on each subband. The UE may report the selected PMI for each subband. In this case, the subband size may be given as shown in the following table 9. In Table 9, if the system bandwidth is set to 6 or 7, this means no application of the subband size. That is, the system bandwidth of 6 or 7 means application of only WB CQI and no subband state.










TABLE 9







System Bandwidth
Subband Size 



NRBDL
(k)









6-7
NA



 8-10
4



11-26
4



27-63
6



 64-110
8










In Table 8, Mode 3-0 and Mode 3-1 show a subband feedback configured by a higher layer.
In Mode 3-0, the UE may report a WB CQI value calculated on the assumption of data transmission on the set-S (total system bandwidth) subbands. The UE may also report one subband CQI value for each subband. The subband CQI value may be calculated on the assumption of data transmission only at the corresponding subband. Even in the case of RI>1, WB CQI and SB CQI may indicate a channel quality for Codeword 1.
In Mode 3-1, a single precoding matrix may be selected from a codebook subset on the assumption of data transmission on the set-S subbands. The UE may report one SB CQI value for each codeword on each subband. The SB CQI value may be calculated on the assumption of a single precoding matrix used in all subbands and data transmission on the corresponding subband. The UE may report a WB CQI value for each codeword. The WB CQI value may be calculated on the assumption of a single precoding matrix used in all the subbands and data transmission on the set-S subbands. The UE may report one selected precoding matrix indicator. The SB CQI value for each codeword may be represented by a differential WB CQI value using a 2-bit subband differential CQI offset. That is, the subband differential CQI offset may be defined as a differential value between a SB CQI index and a WB CQI index. The subband differential CQI offset value may be assigned to any one of four values {−2, 0, +1, +2}. In addition, the subband size may be given as shown in the following table 9.
In Table 8, Mode 2-0 and Mode 2-2 illustrate a UE selected subband feedback. Mode 2-0 and Mode 2-2 illustrate reporting of best-M averages.
In Mode 2-0, the UE may select the set of M preferred subbands (i.e., best-M) from among the entire system bandwidth (set S). The size of one subband may be given as k, and k and M values for each set-S range may be given as shown in the following table 10. In Table 10, if the system bandwidth is set to 6 or 7, this means no application of both the subband size and the M value. That is, the system bandwidth of 6 or 7 means application of only WB CQI and no subband state.
The UE may report one CQI value reflecting data transmission only at the best-M subbands. This CQI value may indicate a channel quality for Codeword 1 even in the case of RI>1. In addition, the UE may report a WB CQI value calculated on the assumption of data transmission on the set-S subbands. The WB CQI value may indicate a channel quality for Codeword 1 even in the case of RI>1.









TABLE 10





System Bandwidth
Subband Size k



NRBDL
(RBs)
M







6-7
NA
NA


 8-10
2
1


11-26
2
3


27-63
3
5


 64-110
4
6









In Mode 2-2, the UE may select the set of M preferred subbands (i.e., best-M) from among the set-S subbands (where the size of one subband is set to k). Simultaneously, one preferred precoding matrix may be selected from among a codebook subset to be used for data transmission on the M selected subbands. The UE may report one CQI value for each codeword on the assumption that data transmission is achieved on M selected subbands and selection precoding matrices are used in each of the M subbands. The UE may report an indicator of one precoding matrix selected for the M subbands. In addition, one precoding matrix (i.e., a precoding matrix different from the precoding matrix for the above-mentioned M selected subbands) may be selected from among the codebook subset on the assumption that data transmission is achieved on the set-S subbands. The UE may report WB CQI, which is calculated on the assumption that data transmission is achieved on the set-S subbands and one precoding matrix is used in all the subbands, for every codeword. The UE may report an indicator of the selected one precoding matrix in association with all subbands.
In association with entirety of UE-selected subband feedback modes (Mode 2-0 and Mode 2-2), the UE may report the positions of M selected subbands using a combination index (r), where r may be represented by the following equation 16.




  
    
      
        r
        =
        
          
            ∑
            
              i
              =
              0
            
            
              M
              -
              1
            
          
          ⁢
          
            
          
          ⁢
          
            〈
            
              
                
                  
                    N
                    -
                    
                      s
                      i
                    
                  
                
              
              
                
                  
                    M
                    -
                    i
                  
                
              
            
            〉
          
        
      
    
    
      
        [
        
          Equation
          ⁢
          
            
          
          ⁢
          16
        
        ]
      
    
  




In Equation 16, the set {si}i=0M-1, (1≦si≦N, si<si+1) may include M sorted subband indexes. In Equation 16,




   
  
    〈
    
      
        
          x
        
      
      
        
          y
        
      
    
    〉
  




may indicate an extended binomial coefficient, which is set to





   
  
    (
    
      
        
          x
        
      
      
        
          y
        
      
    
    )
  




in case of x≧y and is set to zero (0) in case of x<y. Therefore, r may have a unique label and may be denoted by





  r
  ∈
  
    
      {
      
        0
        ,
        ...
        ⁢
        
          
        
        ,
        
          
            (
            
              
                
                  N
                
              
              
                
                  M
                
              
            
            )
          
          -
          1
        
      
      }
    
    .
  




In addition, a CQI value for M selected subbands for each codeword may be denoted by a relative differential value in association with WB CQI. The relative differential value may be denoted by a differential CQI offset level of 2 bits, and may have a value of ‘CQI index—WB CQI index’ of M selected subbands. An available differential CQI value may be assigned to any one of four values {+1, +2, +3, +4}.
In addition, the size(k) of supported subbands and the M value may be given as shown in Table 10. As shown in Table 10, k or M may be given as a function of a system bandwidth.
A label indicating the position of each of M selected subbands (i.e., best-M subbands) may be denoted by L bits, where L is denoted by




  L
  =
  
    
      ⌈
      
        
          log
          2
        
        ⁡
        
          (
          
            
              
                N
              
            
            
              
                M
              
            
          
          )
        
      
      ⌉
    
    .
  




CSI Report Dropping
As described above, CSI corresponding to a downlink channel measurement result obtained by a UE can be reported to an eNB through uplink. Downlink CSI may include an RI, a PMI, a CQI, etc. An advanced wireless communication system that supports an increased number of antennas may use a more accurate precoding matrix than the conventional precoding matrix for accurate downlink channel state feedback. To achieve this, a precoding matrix may be indicated by a combination of two PMIs (referred to as i1 and i2 (or w1 and w2)) and the type of precoding information included in CSI may be indicated using a precoding type indicator (PTI). Here, i1 may be related to channel state with respect to long term and/or wideband whereas i2 may be related to channel state with respect to short term and/or subband. In the case of periodic CSI reporting using a PUCCH, a UE may be semi-statically configured by a higher layer to periodically feed back different CSI (CQI, PMI, RI, PTI) on the PUCCH.
When CSI including a PMI is reported through a PUCCH, PUCCH reporting modes can be classified into two modes according to frequency granularity (i.e. frequency band size as a determination/calculation unit) in which a PMI/CQI is determined/calculated. As shown in Table 5, a mode for reporting a PMI/CQI determined/calculated for wideband can be defined as PUCCH reporting mode 1-1 and a mode for reporting a subband CQI with wideband PMI/CQI can be defined as PUCCH reporting mode 2-1. In the case of CSI reporting through a PUCCH, an RI, a widebank PMI/CQI and a subband CQI are reported at different timings since channel capacity that can be transmitted once through the PUCCH is limited. In this case, the RI is reported in the long term compared to other control information and the wideband PMI/CQI or subband CQI is reported in the short term.
FIG. 22 illustrates control information transmission timing in PUCCH reporting mode 2-1. As shown in FIG. 22, the RI is reported in the long term (that is, less frequently) compared to the WB PMI/CQI. The WB PMI/CQI is reported in the short term compared to the RI and reported in the long term compared to the SB CQI. That is, the SB CQI is reported at a shortest interval (that is, most frequently).
In calculation/determination of CSI, a PMI is determined on the basis of a rank value corresponding to a most recently reported RI and a CQI is determined on the basis of a precoding matrix corresponding to a most recently reported PMI. In the example of FIG. 22, the SB CQI can be calculated on the basis of the most recently reported WB PMI.
A detailed description will be given of CSI report dropping.
CSI report dropping may be determined based on attributes of CSI. For example, the RI is a basis of calculation/determination of other CSI and is transmitted less frequently than other CSI, and thus the RI may be reported and a report of other CSI may be dropped when the timing of reporting the RI collides with the timing of reporting other CSI.
A WB PMI/CQI reporting period and an SB CQI reporting period may be determined based on a predetermined reference period. For example, it is assumed that CSI is reported at intervals of A ms (i.e. A subframes), that is, a predetermined reference CSI reporting period is A ms irrespective of the type of WB PMI/CQI or SB CQI. In this case, the WB PMI/CQI reporting period can be determined as A*(N+1) ms. Here, the SB CQI reporting period can be determined such that the SB CQI is reported N times at intervals of A ms during A*(N+1) ms (i.e. between two consecutive WB PMI/CQI reporting timings). That is, WB PMI/CQI reporting timing and SB CQI reporting timing do not overlap and collision between the WB PMI/CQI and SB CQI and report dropping thereof may not be determined. In the meantime, the RI may be reported in a period corresponding to an integer multiple of the WB PMI/CQI reporting period. That is, the RI reporting period may be determined as A*(N+1)*M. Here, RI reporting timing may be determined according to an offset of B ms based on WB PMI/CQI reporting timing. B may be determined as one value of {0, −1, . . . , −(A−1)}. When B=0, a WB PMI/CQI report may be dropped at the time when the RI is reported.
In a carrier aggregation system, channel measurement and CSI reporting for each downlink cell (or carrier) are needed. CSI about a downlink channel may be reported to an uplink cell (e.g. UL PCell). When two or more serving cells are configured for a UE, the UE transmits CSI about only one serving cell in one subframe. Timing of reporting CSI about each downlink cell may be set according to an independent transmission period per downlink cell. Here, when CSI about a first downlink cell and CSI about a second downlink call are reported to an uplink cell, timing of transmitting the CSI about the first downlink cell may correspond to timing of transmitting the CSI about the second downlink cell (that is, collision may be generated).
To solve this, CSI priority may be set such that CSI having low priority is dropped when CSI having different priorities collide with each other. For example, high priority can be given to information reported in the long term, and thus reporting of latest channel information can be supported. Specifically, a CSI report including an RI (RI, RI+i1 or RI+PTI) or i1 report can have the highest priority. Then, a WB PMI and/or CQI can have higher priority and an SB CQI and/or PMI can have the lowest priority. For example, when a CSI report on the first downlink cell includes RI or i1 and a CSI report on the second downlink cell corresponds to a WB PMI/CQI, the CSI report on the second downlink cell can be dropped. If CSI reports on different serving cells collide with each other while the CSI reports have the same priority, then the CSI report on the serving cell having the lowest index can be dropped.
In the case of PUCCH reporting mode 2-1 in which the RI, WB PMI/CQI and SB CQI are reported through a PUCCH, a WB PMI/CQI report may be dropped for various reasons. When a WB PMI/CQI report is dropped in the PUCCH reporting mode 2-1, calculation/determination of an SB CQI reported at the next timing is incorrect.
FIG. 23 illustrates exemplary CSI reporting to which the present invention is applicable.
FIG. 23 shows an exemplary PUCCH reporting mode in which the RI, WB PMI/CQI and SB CQI are reported. In FIG. 23, only timing for PUCCH reporting is illustrated for clarity. An RI report at PUCCH reporting timing 1 indicates that a rank suitable for downlink channel state is N. Since calculation/determination of the PMI/CQI is performed based on a rank value corresponding to the most recently reported RI, the WB PMI/CQI and SB CQI are all calculated/determined based on the rank N at PUCCH reporting timings 2 to 7. Specifically, a CQI is calculated on the basis of a precoding matrix corresponding to the most recently reported PMI. For example, the SB CQI reported at PUCCH reporting timings 3 and 4 is calculated on the basis of a precoding matrix corresponding to the most recently reported PMI (i.e. PMI reported at PUCCH reporting timing 2) and the PMI reported at PUCCH reporting timing 2 is determined on the basis of the rank N corresponding to the most recently reported RI. Similarly, the SB CQI reported at PUCCH reporting timings 6 and 7 is calculated on the basis of a precoding matrix corresponding to the most recently reported PMI (i.e. PMI reported at PUCCH reporting timing 5) and the PMI reported at PUCCH reporting timing 5 is determined on the basis of rank N corresponding to the most recently reported RI.
When it is assumed that the suitable rank is changed from N to M due to downlink channel state change and thus an RI indicating the rank M is reported at PUCCH reporting timing 8, the subsequent WB PMI/CQI and SB CQI can be calculated/determined on the basis of the rank M corresponding to the most recently reported RI. If the WB PMI/CQI reported at PUCCH reporting timing 9 is dropped (due to high-priority CSI of another downlink cell), then calculation of SB CQI to be reported at PUCCH reporting timing 10 becomes incorrect.
Specifically, if the WB PMI/CQI at PUCCH reporting timing 9 is not dropped, the SB CQI at PUCCH reporting timing 10 will be calculated on the basis of a precoding matrix corresponding to a PMI determined based on the rank M. However, when the WB PMI/CQI at PUCCH reporting timing 9 is dropped, the most recently reported PMI corresponds to the PMI reported at PUCCH reporting timing 5, which is determined based on the rank N. In this case, the SB CQI at PUCCH reporting timing 10 is calculated on the basis of a precoding matrix corresponding to the PMI determined based on the rank N rather than rank M. Accordingly, when the WB PMI/CQI is dropped after the rank is changed, the subsequently reported CQI is calculated based on the unchanged rank rather than the changed rank and thus the CQI cannot correctly indicate the current channel state.
The present invention proposes various schemes for correctly calculating a CQI when a PMI report is dropped after an RI with respect to a change rank is reported.
According to scheme 1, a CQI is calculated on the basis of a PMI determined based on a rank value corresponding to the most recently reported RI when a PMI report is dropped after rank change. Specifically, when a PMI report is dropped after rank change, the CQI can be calculated on the basis of the most recently reported PMI from among PMIs corresponding to the rank value of the most recently reported RI. Referring to FIG. 23, when the WB PMI corresponding to PUCCH reporting timing 9 is dropped, the SB CQI to be reported at PUCCH reporting timing 10 can be calculated on the basis of the most recently reported WB PMI (e.g. the most recently reported WB PMI determined based on the rank M from among WB PMIs reported prior to PUCCH reporting timing 1) from among WB PMIs based on the rank M.
According to scheme 2, a PMI to be used for a predetermined rank is predetermined and a CQI is calculated using the predetermined PMI when a PMI report is dropped after rank change. For example, PMIs can be respectively predetermined for ranks 1, 2, . . . , 8. When the rank is changed from 2 to 1 and a PMI report is dropped after the RI corresponding to the rank 1 is reported, a subsequently reported CQI can be calculated using the PMI predetermined for rank 1.
A PMI predetermined per rank can be defined as follows.
For example, a PMI with a specific index, selected from a codebook corresponding to a set of precoding matrices that can be used for respective ranks, can be defined as the predetermined PMI proposed by the present invention. For instance, a PMI, which will be used when a PMI report is dropped, can be defined as a PMI with the lowest index in the codebook.
Alternatively, a PMI with a specific index, from among PMIs corresponding to respective ranks, defined in codebook subset restriction, can be used as the predetermined PMI according to the present invention. Codebook subset restriction refers to a scheme of selecting/determining a PMI from only some precoding matrices included in a codebook corresponding to a set of precoding matrices that can be used in a wireless communication system and may be used to reduce feedback overhead. A codebook subset may be defined per rank. The codebook subset may be specified by a bitmap parameter set by higher layer signaling. In an embodiment of the present invention, the PMI to be used when a PMI report is dropped can be defined as a PMI with the lowest index in a codebook subset of the corresponding rank.
According to scheme 3, a CQI is calculated on the basis of a rank value corresponding to the most recently reported PMI when a PMI report is dropped after rank change. That is, scheme 3 overrides a rank value corresponding to the most recently reported RI and uses the rank value corresponding to the most recently reported PMI. Referring to FIG. 23, the most recently reported PMI corresponds to the WB PMI reported at PUCCH reporting timing 5, which is determined based on rank N. In this case, the SB CQI to be reported at PUCCH reporting timing 10 can be calculated on the basis of the rank N corresponding to the most recently reported PMI by overriding the rank M indicated by the most recently reported RI (i.e. RI reported at PUCCH reporting timing 9).
According to scheme 4, when a PMI report is dropped after rank change, the dropped PMI report is delayed and reported. FIG. 24 illustrates timing of reporting a dropped PMI report according to an embodiment of the present invention. FIG. 24 shows examples of reporting a dropped PMI at the next transmission opportunity.
For example, the next transmission opportunity for dropped PMI reporting can correspond to the next PUCCH reporting timing. As shown in FIG. 24(a), when a WB PMI/CQI is dropped, the dropped WB PMI/CQI can be transmitted at the next PUCCH reporting timing. That is, PUCCH reporting timing can be predetermined according to a predetermined period as shown in FIG. 22 and a dropped PMI can be reported at the subsequent PUCCH reporting timing. In this case, the dropped PMI instead of CSI destined to be transmitted at the PUCCH reporting timing subsequent to the dropped PMI can be transmitted at the subsequent PUCCH reporting timing. FIG. 24(a) shows a case in which a WB PMI/CQI is dropped at PUCCH reporting timing 2 and the dropped WB PMI/CQI instead of an SB CQI is reported at PUCCH reporting timing 3. In this case, other CSI reports can be transmitted in the predetermined period.
Alternatively, the next transmission opportunity for dropped PMI reporting may correspond to the next subframe. In the example of FIG. 24(b), the WB PMI/CQI dropped at PUCCH reporting timing 2 can be reported in the subframe subsequent to PUCCH reporting timing 2. The subframe subsequent to the PUCCH reporting timing at which the WB PMI/CQI is dropped may not correspond to PUCCH reporting timing preset according to the predetermined period. In this case, CSI to be transmitted at PUCCH reporting timing subsequent to the PUCCH reporting timing at which the WB PMI/CQI is dropped is not affected.
A method for reporting CSI according to an embodiment of the present invention will now be described with reference to FIG. 25.
A UE may report an RI to an eNB in step S2510. A rank value corresponding to the RI reported in step S2510 is changed from a rank value corresponding to an RI reported prior to step S2510.
The UE may drop a PMI report in step S2520. When the PMI report is scheduled according to a CSI reporting period, the PMI report may be dropped due to collision with another CSI report. The dropped PMI may be a WB PMI corresponding to WB PMI/CQI reporting timing in PUCCH reporting mode 2-1. When the PMI report is dropped after RI reporting for the changed rank, incorrect calculation of a CQI can be prevented by applying the schemes proposed by the present invention to CQI calculation/determination.
The UE may report a CQI to the eNB in step S2530. Since the CQI reported in step S2530 is generated as an incorrect value when calculated/determined on the basis of a precoding matrix corresponding to the PMI dropped in step S2520, the CQI may be determined on the basis of a precoding matrix other than the precoding matrix corresponding to the dropped PMI. To determine the other precoding matrix, schemes 1 to 4 according to the present invention are applicable.
In the method for reporting CSI, described with reference to FIG. 25, according to the present invention, the above-described various embodiments may be independently applied or two or more thereof may be simultaneously applied and redundant description is omitted for clarity.
In addition, the principle of the present invention is applicable to CSI feedback for MIMO transmission between an eNB and an RN (on backhaul uplink and backhaul downlink) and MIMO transmission between an RN and a UE (on access uplink and access downlink).
FIG. 26 illustrates a configuration of a transceiver according to an embodiment of the present invention.
Referring to FIG. 26, a transceiver 2610 according to an embodiment of the present invention may include a reception module 2611, a transmission module 2612, a processor 2613, a memory 2614 and a plurality of antennas 2615. The plurality of antennas refers to a transceiver supporting MIMO transmission/reception. The reception module 2611 may receive signals, data and information from an external device and the transmission module 2612 may transmit signals, data and information to the external device. The processor 2613 may control overall operation of the transceiver 2610.
The transceiver 2610 according to an embodiment of the present invention may be a UE that reports CSI on a downlink channel from an eNB. The processor 2613 of the UE may be configured to report an RI through the transmission module 2612. A rank value corresponding to the RI may be changed from a rank value corresponding to the most recently reported RI prior to reporting of the RI. In addition, the processor 2613 may be configured to drop a PMI report after reporting of the RI. Furthermore, the processor 2613 may be configured to report a CQI through the transmission module after dropping of the PMI report. Here, the CQI may be determined on the basis of a precoding matrix other than a precoding matrix corresponding to the dropped PMI.
In addition, the processor 2613 of the transceiver 2610 may process information received by the transceiver 2610, information transmitted from the transceiver 2610 to the outside, etc. The memory 2614 may store processed information for a predetermined time and may be replaced by a component such as a buffer (not shown).
In configuration of the transceiver may be configured such that the above-described various embodiments are independently applied or two or more thereof are simultaneously applied, and redundant description is omitted for clarity.
The above description of the eNB may be equally applied to an RN corresponding to a downlink transmitting entity or an uplink reception entity and the description of the UE may be equally applied to an RN corresponding to a downlink reception entity or an uplink transmission entity.
The embodiments of the present invention may be achieved by various means, for example, hardware, firmware, software, or a combination thereof.
In a hardware configuration, the methods according to the embodiments of the present invention may be achieved by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.
In a firmware or software configuration, the embodiments of the present invention may be implemented in the form of a module, a procedure, a function, etc. For example, software code may be stored in a memory unit and executed by a processor. The memory unit is located at the interior or exterior of the processor and may transmit data to and receive data from the processor via various known means.
The detailed description of the preferred embodiments of the present invention is given to enable those skilled in the art to realize and implement the present invention. While the present invention has been described referring to the preferred embodiments of the present invention, those skilled in the art will appreciate that many modifications and changes can be made to the present invention without departing from the spirit and essential characteristics of the present invention. For example, the structures of the above-described embodiments of the present invention can be used in combination. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. Therefore, the present invention is not intended to limit the embodiments disclosed herein but to give a broadest range matching the principles and new features disclosed herein.
Those skilled in the art will appreciate that the present invention may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims and their legal equivalents, not by the above description, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein. Therefore, the present invention intends not to limit the embodiments disclosed herein but to give a broadest range matching the principles and new features disclosed herein. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by a subsequent amendment after the application is filed.
INDUSTRIAL APPLICABILITY
The above-described method and device for efficiently reporting CSI according to embodiments of the present invention are applicable to various mobile communication systems using multiple antennas.

## Claims

1. A method for a user equipment (UE) to report channel state information (CSI) including at least one of a rank indicator (RI), a precoding matrix indicator (PMI) or a channel quality indicator (CQI) in a wireless communication system, the method comprising:
reporting, by the UE, the RI to an evolved Node B (eNB);
dropping, by the UE, a report of the PMI after the reporting of the RI to the eNB; and
reporting, by the UE the CQI to the eNB after the dropping of the PMI report,
wherein a rank value corresponding to the RI is changed from a rank value corresponding to a most recently reported RI before reporting the RI to the eNB, and
wherein the CQI is determined based on the RI and a precoding matrix other than a precoding matrix corresponding to the dropped PMI report.

2. The method according to claim 1, wherein the CQI is determined based on a precoding matrix corresponding to a PMI having a lowest index, selected from a codebook corresponding to the changed rank value.

3. The method according to claim 2, wherein the PMI having the lowest index is determined in a restricted codebook subset.

4. The method according to claim 1, wherein the CQI is determined based on the changed rank value and a precoding matrix corresponding to a most recently reported PMI from among PMIs reported before reporting the RI.

5. The method according to claim 1, wherein the CQI is determined based on a precoding matrix corresponding to a most recently reported PMI from among PMIs reported before reporting the RI and a rank value corresponding to the most recently reported PMI.

6. The method according to claim 1, further comprising reporting the dropped PMI after dropping the PMI and before reporting the CQI.

7. The method according to claim 6, wherein the dropped PMI is reported at a next reporting opportunity determined according to a CSI reporting period configured for the CSI.

8. The method according to claim 6, wherein the dropped PMI is reported in a subframe subsequent to a subframe in which the PMI report is dropped.

9. The method according to claim 1, wherein the dropping of the PMI is performed when the PMI and another CSI other than the CSI collide.

10. The method according to claim 9, wherein the other CSI is CSI having high priority from among CSI of another cell.

11. The method according to claim 1, wherein the CSI includes RI, wideband PMI and wideband CQI, and subband CQI.

12. The method according to claim 1, wherein the CSI is reported through a physical uplink control channel (PUCCH).

13. The method according to claim 1, wherein the CSI is periodically reported.

14. A user equipment (UE) for reporting channel state information (CSI) including at least one of a rank indicator (RI), a precoding matrix indicator (PMI) or a channel quality indicator (CQI) in a wireless communication system, the UE comprising:
a reception module configured to receive a downlink signal from an evolved Node B (eNB);
a transmission module configured to transmit an uplink signal to the eNB; and
a processor configured to control the reception module and the transmission module,
wherein the processor is further configured to:
report the RI through the transmission module,
drop a report of the PMI after the reporting of the RI through the transmission module, and
report the CQI through the transmission module after the dropping of the PMI report,

wherein a rank value corresponding to the RI is changed from a rank value corresponding to a most the most recently reported RI before reporting the RI through the transmission module, and
wherein the CQI is determined based on the RI and a precoding matrix other than a precoding matrix corresponding to the dropped PMI report.